I 


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ILLINOIS  STATE  GEOLOGICAL  SURVEY 


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ILLINOIS 
STATE   GEOLOGICAL  SURVEY 

F.  W.  DEWOLF,  Director 


BULLETIN  No.  18 


^  Study  of  Sand-Lime  Brick 


BY 

S.  W.  PARR 

AND 

T.  R.  ERNEST 


Urbana 

University  of  Illinois 

1912 


CaSiaME5uHgt> 


Illinois  State  Journal  Co.,  State  Printers 

Springfield,  III. 

1912 


STATE  GEOLOGICAL  COMMISSION. 


Governor  C.  S.  Deneen,  Chairman. 
Professor  T.  C.  Chamberlin,  Vice-Chairman. 
President  Edmund  J.  James,  Secretary. 


Frank  W.  DeWolf,  Director. 


TABLE  OF  CONTENTS. 


Page  . 

Preface 9 

Historical  introduction 11 

General  consideration  of  the  sand-lime  brick  industry 14 

Meaning  of  the  term  sand-lime  brick 14 

The  constituents  of  sand-lime  bricks 15 

The  element  silicon 15 

Silica 15 

Silicic  acids  and  the  silicates 17 

Lime  and  other  calcium  compounds 19 

The  raw  materials  of  the  sand-lime  brick  industry 24 

Sand 24 

Occurences  and  origin 24 

Impurities 25 

Lime .» 26 

Impurities 26 

Burning 27 

Cost  of  burning 27 

Market  grades 28 

Methods  of  testing 29 

Technique  of  the  manufacture  of  sand-lime  bricks 31 

Processes  for  preparing  mixtures 31 

The  hydrated  lime  methods 32 

The  caustic  lime  method 33 

Preparation  of  the  sand 34 

Conclusions 42 

The  effect  of  impurities  in  sand 42 

Pressure  in  molding 44 

Hardening ,. 45 

The  chemistry  of  sand-lime  bricks 47 

Review  of  previous  work 47 

Chemical  investigation 49 

Theoretical 49 

Preparation  of  material  for  analysis 51 

Methods  of  analysis 53 

Results  of  chemical  analyses 54 

Discussion  of  analyses 59 

General  conclusions  as  to  the  constitution  of  sand-lime  bricks 62 

The  physical  texture  of  sand-lime  bricks 63 

Tests  of  sand-lime  bricks ." 65 

Strength  tests 66 

Effects  of  freezing 67 

Tire  resisting  qualities  of  sand-lime  bricks   69 

Description  of  methods  of  testing 70 

Materials  used  in  tests 70 

Apparatus  used  in  tests 71 

Burning 71 

Testing 71 

Method  of  averaging  results 72 

Discussion  of  results 72 

Conclusion 74 

Summary 75 

Bibliography 77 


LIST  OF  ILLUSTRATIONS. 


Plates. 

Page  . 

I.     House  built  of  mortar  bricks  in  1872 30 

II.    Cross-section  of  semi-gas  fired  kiln 28 

III.  Photographs  of  samples  of  bricks 42 

IV.  A  pparatus  used  for  hardening  mixtures  of  lime  and  silica  by  steam 44 

V.    Microphotographs  of  sections  of  sand-lime  bricks. 64 

VI.     Microphotographs  of  sections  of  steamed  lime-silica  mixtures 68 

Figures. 

1.  Le  Chatelier's  curves  of  expansion  of  different  forms  of  silica 17 

2.  Curves  showing  rise  of  temperature  during  hydration  of  lime 30 

3.  Curves  recording  variations  in  modulus  of  rupture  for  bricks  heated  to  different  temperatures.  72 

4.  Curves  recording  variations  in  crushing  strength  of  bricks  heated  to  different  temperatures. .  73 


LETTER  OF  TRANSMITTAL. 


State  Geological  Survey, 
University  of  Illinois,  Feb.  7,  1912. 
Governor  C.  S.  Veneen,  Chairman,  and  Members  of  the  Geological  Com- 
mission : 

Gentlemen — I  submit  herewith  manuscript  for  a  report  entitled, 
A  study  of  sand-lime  brick,  and  recommend  that  it  be  published  as 
Bulletin  Xo.  18.  The  report  was  prepared  by  Prof.  S.  W.  Parr,  con- 
sulting chemist  of  the  Survey,  in  collaboration  with  Dr.  T.  E.  Ernest. 
Xo  sand-lime  bricks  are  now  produced  in  Illinois,  though  the  indus- 
try has  a  footing  in  neighboring  states,  and,  if  we  may  judge  from 
foreign  experience,  will  become  prominent  here  in  the  future. 

Very  respectfully, 

Frank  W.  DeWolf, 

Director. 


PREFACE. 


The  finely  divided  silica  occurring  in  numerous  deposits  in  southern 
Illinois  has  for  some  time  been  the  subject  of  study  in  the  Laboratory 
of  Applied  Chemistry  in  the  University  of  Illinois.  Investigations  upon 
this  material  were  begun  in  the  year  1905  by  Mr.  C.  F.  Hagedorn,  and 
have  been  continued  by  Messrs.  C.  M.  McClure,  W.  S.  Williams/  and 
A.  W.  Beemer.  The  purpose  of  this  work  was  to  determine  the  possi- 
bility and  extent  of  a  reaction  which  might  be  brought  about  between 
the  silica  and  lime  by  means  of  steam  pressure,  somewhat  after  the 
manner  of  the  practice  followed  in  the  manufacture  of  sand-lime  bricks. 
The  extent  of  the  deposits  made  it  appear  probable  that  this  material 
might  find  an  application  in  the  manufacture  of  some  such  ceramic 
product  as  wall  or  floor  tile,  architectural  decorative  material,  or  as  a 
filler  in  sand-lime  bricks. 

The  possible  use  of  the  silica  in  the  manufacture  of  sand-lime  brick 
suggested  the  advisability  of  a  study  of  the  sand-lime  brick  process  from 
both  a  theoretical  and  a  practical  standpoint,  in  order  to  determine  the 
effect  of  substituting  the  silica  for  some  of  the  sand  commonly  used  in 
the  process.  It  seemed  desirable  to  investigate  very  closely  the  chemical 
and  physical  properties  of  compounds  formed  from  finely  divided  silica 
and  lime,  inasmuch  as  these  are  evidently  very  closely  related  to  the 
bonding  material  in  sand-lime  brick,  if,  indeed,  they  are  not  identical 
with  it.  It  had  been  determined  by  the  earlier  experiments  that  when 
mixed  with  lime,  this  silica  enters  into  a  reaction  which  results  in  the 
production  of  a  homogeneous  compound.  This  new  substance,  it  was 
a --umed,  must  resemble  the  film  of  hydrated  calcium  silicate  surround- 
ing the  sand  grains  in  sand-lime  bricks. 

That  good  bricks  can  be  made  from  sand  and  lime  is  no  longer  ques- 
tioned. The  matter  of  cost  of  their  manufacture,  however,  should  be 
carefully  determined  for  any  locality  at  which  it  is  proposed  'to  erect  a 
plant,  in  order  to  avoid  the  mistake  of  building  in  a  situation  where  the 
manufacture  of  the  bricks  is  not  economically  practicable. 

Illinois  is  no  longer  represented  in  the  list  of  states  producing  sand- 
lime  bricks,  although  there  are  in  it,  doubtless,  many  localities  in  which 
their  manufacture  would  be  profitable  both  to  the  producer  and  to  the 
consumer.  It  seems  fitting,  therefore,  that  some  information  relative  to 
this  industry  should  be  published  by  the  State  Geological  Survey.  It 
is  the  purpose  of  this  bulletin  to  discuss  briefly  the  chemistry  of  sand- 


i  Bull.  111.  State  Geol.  Survey,  No.  14,  1909,  p.  275. 


10  STUDY   OF    SAND-LIME   BRICK. 

lime  bricks  and  the  conditions  that  are  most  favorable  for  the  produc- 
tion of  bricks  of  good  quality.  Incidentally,  the  results  of  several  series 
of  tests  on  commercial  bricks  are  given. 

In  the  preparation  of  this  bulletin  the  authors  wish  to  acknowledge 
gratefully  the  services  rendered  them  by  the  Anderson  Foundry  and 
Machine  Company  in  the  use  of  their  experimental  plant  for  the  manu- 
facture of  sand-lime  bricks;  to  Mr.  E.  T.  Stull,  of  the  Department  of 
Ceramics  of  the  University  of  Illinois,  for  the  use  of  kiln  and  accessories 
in  fire  tests;  to  Prof.  A.  N.  Talbot,  Mr.  D.  A.  Abrams,  and  Mr.  A.  E. 
Lord,  of  the  Laboratory  of  Applied  Mechanics  of  the  University  of 
Illinois,  for  assistance  given  in  testing,  and  for  the  use  of  the  facili- 
ties of  the  laboratory;  to  Prof.  W.  S.  Bayley,  for  valuable  suggestions 
in  the  use  of  the  polarizing  microscope;  to  the  United  States  Brick 
Corporation  and  the  Excelsior  Brick  Company,  of  Michigan  City, 
Indiana,  for  samples  of  bricks  used  in  some  of  the  tests,  and  to  Mr. 
E.  B.  Stephenson,  of  the  Chemical  Laboratory  of  the  University  of 
Illinois,  for  assistance  in  making  photomicrographs. 


ILLINOIS  STATE  GEOLOGICAL  SURVEY. 


Bull.  No.  18,  Plate  I. 


House  built  of  mortar  brick  in  1872. 


11 


HISTORICAL  INTRODUCTION 


The  manufacture  of  building  bricks  from  mixtures  of  sand  and  lime 
began  more  than  half  a  century  ago,  but  the  modern  methods  of  manu- 
facture are  of  much  more  recent  origin.  The  first  bricks  prepared  from 
sand  and  lime  have  been  properly  called  "mortar  bricks/'  for  in  reality 
they  consisted  of  nothing  more  than  common  lime  mortar  molded  into 
bricks  and  allowed  to  harden  by  the  absorption  of  carbonic  acid  from 
the  atmosphere.  In  this  process  it  was  necessary  to  use  enough  lime  to 
surround  the  sand  grains  and  give  a  more  or  less  plastic  mortar  which 
could  be  molded  in  a  manner  similar  to  the  soft-mud  process  for  making 
clay  brick.  The  amount  of  lime  used  varied  from  20  to  40  per  cent, 
depending  on  its  quality.  The  hardening  was  due  to  the  formation  of 
calcium  carbonate,  and,  when  finished,  the  bricks  consisted  of  grains  of 
sand  embedded  in  a  sort  of  artificial  limestone.  There  was  no  appre- 
ciable union  of  the  sand  grains  chemically,  but  they  were  held  in  place 
by  a  network  of  calcium  carbonate;  or,  if  very  much  lime  was  used,  it 
is  perhaps  more  exact  to  speak  of  the  sand  particles  as  being  embedded 
in  a  mass  of  calcium  carbonate.  The  sand  served  the  purpose  of  pre- 
venting the  brick  from  shrinking  on  drying,  and  at  the  same  time,  it 
reduced  the  amount  of  lime  required  in  the  mixture,  just  as  the  rock, 
sand,  and  other  fragmental  material  in  concrete,  reduce  the  amount  of 
cement  required  in  it. 

The  objections  to  "mortar  bricks"  are  obvious,  and  it  is  not  surpris- 
ing that  the  bricks  were  used  only  in  regions  where  the  soil  was  sandy, 
and  clays  for  making  other  kinds  of  bricks  could  not  be  found.  More- 
over, the  large  percentage  of  lime  required  in  their  manufacture  and  the 
long  time  necessary  for  hardening  them,  especially  in  wet  seasons,  made 
them  too  costly  to  compete  with  common  bricks.  Notwithstanding  these 
difficulties,  however,  bricks  made  by  the  mortar  process  possessed  won- 
derful strength  and  durability.  Plate  I  is  the  picture  of  a  building 
erected  half  a  century  ago  in  which  material  of  this  character  was  used.1 
It  illustrates  the  remarkable  durability  of  properly  made  "mortar 
bricks." 

In  order  to  hasten  the  hardening  of  the  mortar  bricks  it  became  the 
practice  to  store  them  in  enclosed  sheds  and   to  enrich  the  atmosphere 


i  The  presenl  occupant  of  the  house  says:  "  For  your  information,  will  say  thai  il  is  a  two-story  house 
built  of  sand-lime  brick.  4  by  5  by  10  inches,  in  1872.  Not  a  brick  in  the  entire  building  has  shown  the 
ieast  deterioration  up  to  the  present  time." 


12  STUDY   OF    SAND-LIME   BRICK. 

with  carbonic  acid.  Afterward,  steam  and  carbonic  acid  were  delivered 
into  the  curing  sheds  and  the  time  required  for  hardening  was  thereby 
further  shortened.  This  latter  procedure  resulted  in  the  formation  of 
a  bond  composed  of  both  calcium  carbonate  and  hydrated  calcium  sili- 
cate, thus  yielding  bricks  superior  to  those  produced  by  the  original 
process  in  which  the  bond  was  exclusively  carbonate. 

In  1831  Dr.  W.  Michaelis  took  out  a  patent  (D.  R.  P.  Nr.  14195) 
for  hardening  mixtures  of  lime  and  sand  by  high  pressure  steam.  This 
is  briefly  described  as  follows:  "High,  pressure  steam  is  allowed  to  act 
for  a  number  of  hours  upon  a  mixture  of  10  to  40  parts  lime  (or  barium 
or  strontium  hydrate)  with  100  parts  sand  (or  minerals  containing 
silicic  acid)  at  a  temperature  from  130°  to  300°  C,  in  a  specially  con- 
structed apparatus.  There  results  a  silicate  which  forms  a  hard,  air- 
and-water-resisting  mass."  The  patent  lapsed  before  any  commercial 
use  had  been  made  of  it.  Like  many  other  inventions,  this  one  probably 
failed  to  be  of  value  because  of  a.  lack  of  development  in  some  related 
industry.  For  instance,  it  was  not  until  the  engineer  and  chemist  had 
improved  the  methods  of  steel  manufacture  so  that  cylinders  in  which 
the  bricks  are  hardened  could  be  constructed  of  sufficient  strength  to  bear 
the  burden,  that  the  manufacture  of  the  bricks  was  possible  on  a  com- 
mercial scale. 

In  1896  there  were  in  Germany  several  plants  in  operation  using  the 
process  patented  by  Dr.  Michaelis,  but  it  was  not  until  the  year  1898 
that  sand-lime  bricks  were  produced  on  a  large  scale  even  in  that 
country.  From  this  date,  however,  to  the  present  time  the  industry  has 
there  enjoyed  a  healthy  growth.  In  the  beginning  of  July,  1908,  there 
were  285  German  sand-lime  brick  plants,  producing  from  900  to  1300 
million  sand-lime,  bricks  annually.  As  is  usually  the  case  with  new 
materials  of  construction,  considerable  trouble  was  experienced  in 
marketing  the  product.  There  was  at  first  a  great  deal  of  prejudice 
against  the  new  bricks  on  the  part  of  architects  and  contractors,  and 
perhaps  justly  so,  but  this  has  now  almost  completely  disappeared.  The 
new  material  has  won  favor  with  the  German  Government,  so  that  now 
in  government  work  sand-lime  bricks  are  not  only  tolerated  but  actually 
specified  in  many  cases.  The  Venn  cler  Kalksandsieinfabriken  has  done 
much  to  remove  this  prejudice  by  disseminating  information,  making 
tests,  standardizing  specifications,  etc.  The  industry  is  well  enough 
advanced  in  Germany  to  support  a  publication  devoted  to  its  interests. 

Other  countries  soon  followed  the  example  of  Germany.  In  the 
United  States  the  first  plant,  that  of  the  Olemacher  Brick  Company,  was 
built  in  Michigan  City,  Indiana,  in  the  year  1901 ;  and  in  1902  there 
were  five  factories  in  operation,  with  a  total  daily  output  of  about 
100,000  bricks.  It  is  reported  that  the  sales  during  this  year  were 
6,000,000  bricks.  The  first  reliable  statistics  of  the  sand-lime  brick 
industry  were  collected  by  the  United  States  Geological  Survey  for  the 
year  1903.  Succeeding  years  show  a  very  rapid  increase  in  the  number 
of  bricks  made,  until  the  year  1907,  when,  of  course,  all  industry  was 


HISTORICAL    INTRODUCTION. 


13 


checked  owing  to  the  financial  condition  of  the  country.  The  following 
table  will  show  the  production  in  the  United  States,  as  reported  by  the 
Geological  Survey.1 


Table  1 — Production  of  sand-lime  brick  in  the  United  States. 


Year. 

Number 

of 
plants. 

Value 

of 

product. 

Prices  per  M. 

Common. 

Face. 

Fancy. 

1901 

1 
5 
16 
57 
84 
87 
94 
87 
74 

1902 

1903. . . 

$     155.040 

463,128 

973,064 

1, 170. 005 

1,225,769 

953,552 

1,046,184 

1904 

1905 

1906 

$6  71 
6  61 
6  33 

6  39 

310    V2 

10  96 
12  16 

11  98 

1907 

1908 

1909 

$25  (.6 
27  13 

The  development  of  the  industry  in  this  country  has  been  very  satis- 
factory. There  are,  however,  some  localities  in  which  the  manufacturer 
finds  difficulty  in  marketing  his  product,  because  of  prejudice  on  the 
part  of  architects.  The  American  industry  is  greatly  in  need  of  more 
publicity,  but  this  publicity  should  be  of  the  right  kind,  and  free  from 
exaggerations  such  as  are  to  be  found  in  the  advertising  literature  of 
some  promoters.  There  is  an  organization  of  the  manufacturers  of 
sand-lime  bricks  which  is  known  as  The  American  Sand-Lime  Brick 
Manufacturers'  Association,  which  will  doubtless  perform  a  work  cor- 
responding to  that  of  the  Kalksandsteinfabricken  of  Germany.  A  good 
publication  devoted  to  the  industry  is  very  greatly  needed,  and  it  is  to 
be  hoped  that  one  will  soon  be  established,  in  order  that  the  literature 
relating  to  all  phases  of  the  sand-lime  brick  manufacture  may  be  avail- 
able in  a  single  publication. 


1  Middleton,  Jefferson:    Mineral  Resources  U.  S.  for  1909,  U.  S.  Geological  Survey,  1911,  p.  551. 


14  STUDY   OF   SANDrLlME   BRICK. 


GENERAL  CONSIDERATION  OF  THE  SAND 
LIME  BRICK  INDUSTRY. 


Meaning  of  the  Term  "Sand-Lime  Brick/' 

Sand-lime  brick  or  the  "Kalksandstein"  of  the  Germans,  may  be 
defined  as  a  mass  of  sand  grains  cemented  together  by  hydrated  calcium 
silicate.  If  the  lime  used  in  the  manufacture  is  dolomitic  there  will  be 
in  the  bond  hydrated  magnesium  silicate  as  well  as  calcium  silicate, 
but  experience  has  shown  that  the  best  product  is  obtained  when  the 
percentage  of  magnesium  oxide  in  the  lime  is  low.  The  reaction 
between  lime  and  silica  resulting  in  the  formation  of  hydrated  lime 
silicates  takes  place  slowly  at  ordinary  temperatures  in  moist  atmos- 
pheres, but  in  practice  it  is  hastened  by  the  action  of  steam.  Sand-lime 
brick  differs  from  sandstone,  mortar,  and  silica  brick  primarily  in  the 
nature  of  the  bond. 

Sandstone  is  formed  from  beds  of  sand  which  have  been  laid  down 
and  covered  by  later  strata.  The  sand  is  first  closely  packed  by  the 
pressure  of  the  strata  above.  The  cementation,  or  formation  of  bond, 
then  begins,  and  is  effected  by  the  deposition,  in  the  interstices  between 
the  sand  grains,  of  various  chemical  substances  that  may  be  carried  in 
solution  .by  percolating  water.  Such  substances  are  calcium,  magnesium, 
and  iron  carbonates ;  calcium,  barium  and  strontium  sulphates ;  etc. 
The  bond  in  the  sandstone  is  purely  a  mechanical  one,  and  the  stone 
possesses  its  strength,  its  power  of  resistance  to  frost,  heat,  etc.,  by 
virtue  of  its  compactness. 

In  the  case  of  mortar,  mortar  brick,  etc.,  the  sand  and  one  consti- 
tuent of  the  bonding  material  are  incorporated  at  the  time  of  prepara- 
tion of  the  mixture.  In  order  that  the  mass  may  harden,,  it  is  necessary 
that  another  constituent,  viz:  carbonic  acid,  be  added  to  change  the 
soluble  calcium  hydroxide  into  the  insoluble  carbonate.  This  is  obtained 
from  the  atmosphere.  The  bond  in  this  case  is  almost  entirely  mechan- 
ical, as  it  is  in  the  case  of  natural  sandstone. 

Hydraulic  mortars  differ  from  ordinary  lime  mortars  in  that  they  are 
capable  of  hardening  without  the  addition  of  carbonic  acid.  The  bond 
in  this  mortar  consists  of  silicates  and  aluminates  of  calcium  and. 
magnesium,  but  there  is  no  appreciable  chemical  reaction  taking  place 
between  the  silica  of  the  sand  and  any  of  the  bonding  constituents.  The 
bond  in  this  case  is  mechanical,  as  before. 


CONSTITUENTS   OF   SAND-LIME  BRICKS.  15 

The  material  of  silica  bricks  resembles  that  of  sand-lime  bricks  more 
closely,  perhaps,  than  does  any  other  material.  Silica  bricks  are  made 
quite  extensively  for  use  as  refractory  linings  for  furnaces.  They  con- 
sist of  sand  grains  cemented  together  by  true  calcium  silicate.  They 
are  prepared  by  mixing  lime  and  silica  in  the  proportion  of  about  3-4 
per  cent  of  the  former  to  96-97  per  cent  of  the  latter,  subjecting  to 
great  pressure  in  molding,  and  burning  at  a  rather  high  temperature. 
The  lime  reacts  with  the  silica  of  the  sand  forming  a  kind  of  glass 
which  cements  the  sand  grains  together.  The  difference  between  a 
silica  brick  and  the  common  sand-lime  brick  is  that  in  the  former  littld 
lime  is  used,  and  the  hardening  is  done  by  firing  in  a  kilri ;  while  sand- 
lime  bricks  contain  much  more  lime  and  they  are  hardened  by  the  action 
of  saturated  steam  under  pressure.  In  silica  bricks  the  bond  consists 
of  a  glass  containing  no  water;  while  in  the  case  of  sand-lime  bricks, 
the  bond  is  not  a  glass  but  a  hydrated  silicate,  very  much  akin,  no  doubt, 
to  some  of  the  constituents  of  set  Portland  cement. 

The  Constituents  of  Sand-Lime  Bricks. 

Exclusive  of  the  impurities  always  found  in  the  raw  materials  of  sand- 
lime  bricks,  their  primary  constituents  are  silica  (Si02),  lime  (CaO), 
and  water  (H20).  Inasmuch  as  any  industrial  process  can  be  only 
imperfectly  understood  without  a  knowledge  of  the  chemistry  of  the 
materials  used  in  the  process,  it  seems  well  to  discuss  briefly,  at  this 
point,  the  chemistry  of  silica  and  lime. 

THE  ELEMENT   SILICON. 

The  element  silicon  exists  in  many  forms  in  the  earth's  crust  of  which 
it  constitutes  about  28  per  cent  by  weight.  It  is  never  found  free,  but 
always  combined  with  oxygen  to  form  silica  (Si02),  or  with  oxygen 
and  metalic  oxides  to  form  silicates,  of  which  feldspar  (K203.Ala03. 
C>Si02),  and  kaolin   (Al203.2Si02.2H20)   are  typical. 

The  element  silicon  is  of  interest  only  theoretically.  It  can  be  pre- 
pared from  several  of  its  compounds  without  much  difficulty,  and,  when 
free,  exists  in  several  allotropic  forms,  as  does  carbon  in  charcoal  and 
diamond.  It  combines  very  energetically  with  many  substances.  At 
ordinary  temperatures  fluorine  unites  with  it  to  form  silicon  tetra- 
fluoride.  It  is  attacked  by  chlorine,  bromine,  and  nitrogen  at  430°, 
560°,  and  1000°,  respectively.  When  heated  to  400°  in  the  air,  it  burns, 
forming  a  white  powder,  Si02  or  silica,  the  principal  constituent  of  sand- 
lime  bricks. 

SILICA   (Si02). 

This  compound  occurs  as  sand  in  all  soils.  It  is  removed  from  them 
by  running  water  and  is  deposited  in  the  beds  of  streams  and  on  the 
bottoms  of  the  oceans,  and  is  later  compacted  into  great  masses  of  sedi- 
mentary rock,  called  sandstone.  Silica  is  found  also  in  granite  and 
other  igneous  rocks,  as  quartz,    having    crystallized    from    the    molten 


16  STUDY    OF    SAND-LIME   BRICK. 

magma  which,  upon  cooling,  made  the  rocks;  and  is  present  in  many 
veins,  where  it  was  crystallized  from  solutions.  Flint  is  a  variety  found 
in  chalk  deposits. 

Crystalline  silica  exists  in  two  forms,  viz,  quartz  and  tridymite.  These 
two  minerals  resemble  one  another  very  closely.  Both  crystallize  in 
the  hexagonal  system,  are  optically  positive,  and  have  a  hardness  of 
about  7  (according  to  Moll's  scale).  Both  are  colorless  to  white,  brittle, 
and  have  a  conchoidal  fracture.  In  specific  gravity,  •  however,  there  is 
a  marked  difference;  that  of  quartz  beinng  2.66,  while  that  of  tridymite 
is  2.28  to  2.33.  Moreover,  tridymite  is  soluble  in  boiling  sodium  car- 
bonate, while  -quartz  (unless  very  finely  divided)  is  not. 

Of  these  two  crystalline  varieties  of  silica,  quartz  is  stable  at  ordi- 
nary temperatures,  while  tridymite  is  the  stable  form  at  temperatures 
above  800°  C.  Consequently,  tridymite  crystallizes  from  fusions  at  high 
temperatures  and  quartz  at  temperatures  below  800°.  When  quartz  is 
heated  to  temperatures  above  800°  it  becomes  unstable  and  begins  to 
change  into  tridymite.  The  change  proceeds  slowly,  however,  so  that 
it  is  possible  to  study  the  properties  of  quartz  much  above  the  temper- 
ature at  which  it  ceases  to  be  the  stable  modification.  The  reverse 
transformation  is  also  quite  sluggish,  so  that  by  sudden  cooling  it  is 
possible  to  have  tridymite  at  ordinary  temperatures  even  though  it  is 
not  the  stable  form. 

The  purest  forms  of  silica  are  colorless  and  fuse  at  a  temperature  of 
about  1700°  C.  When  fused  and  allowed  to  cool  quickly  it  does  not 
crystallize,  but  is  known  as  quartz  glass.  Quartz  glass  has  the  very 
remarkable  property  of  being  able  to  withstand  sudden  changes  of  tem- 
perature without  being  fractured.  Vessels  made  of  this  material  may 
be  heated  to  redness  and  quenched  in  water  without  fracture.  Le  Chate- 
lier1  studied  the  expansion  of  various  forms  of  silica  at  temperatures 
ranging  from  atmospheric  to  1050°  C.  The  results  of  his  investiga- 
tions are  shown  graphically  in  figure  1. 

The  molecular  changes  expressed  by  the  expansion  shown  in  these 
curves  are  of  great  significance  in  many  industrial  processes.  In  the 
manufacture  of  silica,  or  Dinas  bricks  great  difficulty  is  experienced  in 
properly  hardening,  owing  to  these  changes.  It  is  also  due  to  their  great 
expansibility  that  silica  bricks  are  unfit  for  use  in  places  where  they 
must  be  heated  and  cooled  frequently.  Bricks  made  from  clays  high  in 
sand  are  found  to  expand  to  such  an  extent  in  the  kiln  that  much  care 
must  be  used  in  heating  up  and  cooling  clown  the  ware  made  from 
them.  '  In  a  fire  test  on  sand-lime  bricks,  as  will  be  shown  later,  it  was 
found  that  in  the  neighborhood  of  500°  there  was  a  weakening  of  the 
bricks,  due,  no  doubt,  to  this  sudden  expansion  of  the  quartz.  In  the 
preparation  of  potters,  flint,  quartz  rock  is  calcined  and  quenched  before 
grinding.  The  volume  changes  produced  by  the  sudden  chilling  causes 
the  rock  to  be  filled  with  a  very  close  network  of  minute  cracks,  and 
consequently  to  grind  much  easier  than  a  raw  quartz. 


i  Compt.  Rend,  de  L' Academy  des  Sciences,  108,  1899,  p.  1046,  and  109,  1S99,  p.  204. 


CONSTITUENTS    OF   SAND-LIME   BRICKS. 


17 


^  Fused  quartz,  opal  and  precipitated  silica  are  forms  of  amorphous 
silica,  which  is  characterized  by  the  fact  that  its  properties  are  inde- 
pendent of  the  directions  along  which  forces  act.  In  quartz  and  tridy- 
mite,  for  example,  the  coefficients  of  expansion  and  of  conductivity,  the 
indices  of  refraction,  etc.,  are  different  in  different  directions,  whereas 
in  amorphous  silica  they  are  the  same  in  all  directions.     Further,  when 


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Fig.    1.      Le    Chatelier's    curves,    showing    expansion    of    different    forms    of 
silica  from  25°C.  to  1050°C. 

thin  plates  cut  from  opal  and  quartz  are  placed  under  the  polarizing 
microscope  between  crossed  nicols,  and  rotated,  no  color  changes  are 
observed  in  the  opal,  whereas,  the  quartz  may  show  various  colors, 
changing  with  the  rotation  of  the  plate. 

SILICIC   ACIDS   AND   THE  SILICATES. 

All  varieties  of  silica,  when  heated  with  metallic  compounds,  combine 
with  the  metals  at  some  temperature  to  form  silicates.  Thus  a  mixture 
of  silica  and  sodium  carbonate,  hydrate  or  oxide,  when  sufficiently 
heated,  fuses  to  a  liquid  mass,  which,  when  cooled,  dissolves  in  water 
as  soluble  sodium  silicates.  On  the  addition  of  acids,  these  silicates  are 
decomposed  with  the  liberation  of  more  or  less  silicic  acid,  and  the 
formation  of  a  sodium  salt  of  the  acid  used.  Silicic  acid  is  very  weak 
when  considered  from  the  standpoint  of  its  ability  to  furnish  hydrogen 
ions,  or  its  ability  to  liberate  otber  acids  from  their  salts,  or  to  resist 


—2  G 


18  STUDY   OF    SAND-LIME   BRICK. 

such  liberation  by  other  acids  in  solution.  When  lime  is  added  to  silicic 
acid  in  solution,  a  precipitate  is  formed,  which  is  calcium  hydrosilicate. 
This  is  the  principal  ingredient  .in  set  Puzzolan  cements.  When  car- 
bonic acid  gas  is  passed  through  water  containing  this  compound  in 
suspension,  the  calcium  silicate  is  decomposed  with  the  formation  of 
calcium  carbonate  and  the  liberation  of  silicic  acid.  This  phenomenon 
is  also  observed  when  many  other  weak  acids  are  allowed  to  act  on 
hydrated  calcium  silicates,  thus  showing  the  feebleness  of  some  of  the 
hydrated  silicic  acids. 

At  high  temperatures,  on  the  other  hand,  silicic  acid  is  one  of  the 
strongest  acids  known,  and  is  able  to  replace  many  acids  from  their 
salts.  This  is  shown  in  fusions  of  silica  and  sodium  carbonate  by  the 
escape  of  carbonic  acid  gas.  Again,  in  the  formation  of  salt  glazes, 
salt  is  thrown  into  the  kiln.  This  volatilizes,  and,  coming  into  contact 
with  the  hot  ware,  is  decomposed,  the  base  being  retained  by  the  silica, 
while  the  chlorine  passes  out  with  the  flue  gases.  Ordinary  glass  is  a 
mixture  of  silicates  formed  by  fusion.  It  resists  the  action  of  all  acids 
except  hydrofluoric.  Thus,  under  some  conditions,  silicic  acid  forms 
salts  that  are  among  the  weakest  known,  while  under  others  it  forms 
compounds  that  are  very  durable. 

One  other  class  of  silicates  that  deserve  mention  at  this  point  are 
those  that  set  or  harden  when  wet  with  water.  A  good  representation 
of  this  class  is  the  dicalcium  silicate  (Ca2Si04)  found  in  Portland 
cement.  This  compound  may  be  formed  by  fusing  lime  and  silica  in  the 
proportions  indicated  in  the  formula.  It  exists  in  several  allotropic 
modifications,1  distinguished  as  the  Alpha,  Beta,  and  Gamma  varieties. 

The  Gamma  variety  is  the  stable  form  at  temperatures  above  1400°, 
the  Beta  between  1400°  and  700°,  and  the  Alpha  below  700°.  When 
treated  with  water  all  varieties  are  hydrolized  with  the  formation  of 
calcium  hydroxide  and  silicic  acid,  thus : 

Ca2Si04+4H20^2Ca(OH)2+H4Si04. 

The  calcium  hydroxide  and  silicic  acid  may  ■  react  under  favorable 
conditions  to  form  a  hydrated  calcium  silicate,  thus : 

Ca  (OH)  2+H4Si04=CaSi03.H20+2H20. 

The  compounds  of  silicic  acid  found  in  nature  are  varied  and  numer- 
ous. When  a  silicate  such  as  the  dicalcium  silicate  mentioned  above, 
or  sodium  silicate,  formed  by  the  fusion  of  silica  and  sodium  carbonate, 
is  treated  with  an  acid,  orthosilicic  acid  (H4Si04)  is  formed.  By  care- 
fully drying,  this  can  be  deprived  of  half  its  water,  when  metasilicic 
acid  results. 

H4Si04+H20=H2Si03. 

By  the  elimination  of  water  from  2,  3,  and  4  molecules  of  the  ortho- 
acid,  it  is  possible  to  imagine  the  formation  of  a  large  series  of  acids. 
The  following  is  a  list  of  hypothetical  acids  whose  salts  are  widely  dis- 
tributed in  the  silicate  minerals. 


iJour.  Am.  Chem.  Soc.  Vol.,  28,  1906,  p.  1059. 


CONSTITUENTS   OF   SAND-LIME  BRICKS. 


19 


Table  2 — List  of  hypothetical  silicic  acids,  with  their  formulas. 


Formula. 

Name. 

Basicity. 

H4SiO< 

Orthosilicic  acid 

4 

H2Si03 

Motasilicic  acid 

2 

HoSi.O^ 

Metadisilicic  acid •. 

2 

HsSioO: 

Orthodisilicic  acid 

6 

H2Si307 

2 

H4Si308... 

4 

8 

H«Si409 

Tetrasilicic  acid 

2 

H6Si40n... 

6 

Hi0Si4Oi3 

Tetrasilicic  acid 

10 

The  following  table  is  a  list  of  typical  minerals  and  their  correspond- 


ing silicic  acids : 


Orthosilicates 
(H4Si04) 

Metasilicates 
(H2Si03) 

Orthodisilicate 
(H6Si207) 


Minerals  and  their  silicic  acids. 


Trisilicate 
(H,Si3Os) 


Garnet, 

Mica, 

Kaolin, 

Wollastonite, 

Beryl, 

Enstatite, 

Serpentine, 
Orthoclase, 


Ca3Fe2(Si04)3 

KH,Al,(Si04)8 

H2Al2(Si04)2H20 

CaSiO:j 

Gl3Al2(Si03)fi 

MgSi03 

Mg3Si20T 
KAlSiA 


LIME  AND  OTHER   CALCIUM   COMPOUNDS. 

This  very  important  constituent  of  sand-lime  bricks  is  an  oxide  of 
the  metal  calcium,  some  of  the  compounds  of  which  are  found  in  large 
quantities  in  nature.  It  exists  principally  in  combination  with  car- 
bonic acid  as  calcium  carbonate.  The  purest  form  of  calcium  carbonate 
is  known  as  calcite,  which  in  some  localities  is  found  in  a  state  of  almost 
absolute  purity.  Aragonite  is  another  form  of  crystallized  calcium  'car- 
bonate, less  widely  distributed  than  calcite.  The  sources  of  the  calcium 
carbonate  for  use  in  lime  burning  are  the  rocks,  marble  and  limestone. 
These  vary  widely  in  the  degree  of  purity  in  which  they  are  found. 
Impure,  clay-containing  limestone  and  marls  are  used  extensively  in 
the  manufacture  of  hydraulic  limes  and  cements. 

Metallic  oxides  vary  widely  in  their  ability  to  hold  carbon  dioxide. 
The  carbonates  of  silver,  mercury,  iron,  and  lead  decompose  quite  readily 
giving  off  carbon  dioxide  with  the  formation  of  the  oxides,  while  the 
carbonates  of  the  alkali  metals  (sodium  and  potassium)  volatilize  with- 
out decomposition.  When,  however,  calcium  carbonate  is  enclosed  in  a 
tube  and  heated  in  a  vacuum,  it  is  found  to  give  definite  pressures,  vary- 
ing with  the  temperature.  The  dissociation  of  calcium  carbonate  was 
first  studied  by  Debray,1  who  observed  the 'pressures  corresponding  to 
the  boiling  or  melting  points  of  variou>  substances.  The  results  of  his 
work  for  calcium  carbonate  were  as  follows: 


Compt.  Rend.  Vol.  64,  <Kr>7,  p.  603. 


20 


STUDY    OF    SAND-LIME   BRICK. 


Table  3 — Vapor  pressures  of  CaC03  at  various  temperatures,  according 

to  Deoray. 


Temperature  in  degrees  centigrade. 

Pressure  in  mm.  of  mercury . 

350 

Imperceptible 

440 

860 

85 

1040 .• 

520 

Le  Chatelier  took  up  the  problem  twenty  years  later  (1887),  after 
the  invention  of  his  thermo-electric  couple.  By  means  of  this  he  was 
able  to  measure  temperatures  more  accurately  than  was  Debray,  and 
furthermore,  to  make  his  curve  continuous  over  the  range  of  temper- 
atures studied.  His  work  has  proved  a  classic,  and  is  today  among  the 
best  in  this  field.     His  results  are  shown  in  the  following  table : 

Table   4 — Dissociation   pressures   of   calcium    carbonate,   according    to 

Le  Chatelier. 


Temperature,  in  degrees  centigrade. 


Pressure  in  mm.  of  mercury. 


547 

27                                                                      

610 

46 

625 

56...                                                          

740 

255...                                                               

745 

289                                                                        

810 

678 

812 

753 

865 

1333 

In  1897  A.  Herzfeld1  worked  along  a  somewhat  different  line.  He 
heated  calcium  carbonate  in  an  atmosphere  of  carbon  dioxide,  and  noted 
the  temperature  at  which  the  carbonate  began  to  lose  weight.  He  came 
to  the  conclusion  that  at  900°  the  dissociation  pressure  of  calcium  car- 
bonate is  less  than  one  atmosphere. 

Otto  Brille2  (1905)  employed  the  same  method  as  did  Herzfeld,  but 
arrived  at  different  conclusions.  According  to  this  investigator,  the 
temperature  at  which  the  dissociation  pressure  of  calcium  carbonate  is 
equal  to  an  atmosphere  is  825°. 

The  latest  work  on  the  subject  is  that  of  D.  Zavrieff,3  who  carried  out 
a  series  of  very  carefully  conducted  measurements,  and  arrived  at  the 
conclusion  that  910°  to  920°  is  the  temperature  at  which  the  dissocia- 
tion pressure  of  calcium  carbonate  is  equal  to  an  atmosphere;  and  of 
E.  H.  Eeisenfeld,4  who  finds  that  at  700°,  800°  and  900°  the  dissocia- 
tion pressures  are  respectively  50.4  mm.,  195  mm.  and  700  mm.  In 
the  light  of  this  recent  work,  it  appears  to  be  advisable  to  adopt  900° 
as  the  temperature  of  rapid  decomposition  of  calcium  carbonate. 


1  Zeitschr.  fur  Rubenz  Ind.,  1897,  p.  820. 

2  Zeitschr.  fur  anorg.  Chem.,  vol.  45,  1905,  p.  275. 

3  Jour,  de  chimie  physique,  vol.  7,  1909,  p.  31 

4  Jour,  de  chimie  physique,  vol.  7,  1909,  p.  561. 


CONSTITUENTS   OF   SAND-LIME  BRICKS.  21 

As  viewed  in  the  light  of  the  phase  rule,  we  have  in  the  equilibrium 
CaC03±^CaO+C02— 43'J  11  cal.  a  univariant  system,  by  which  we  mean 
that  a  change  in  the  temperature  of  the  system  necessitates  a  corres- 
ponding change  in  pressure  and  vice  versa.  If  the  temperature  is  kept 
constant,  reduction  of  the  pressure  of  the  carbon  dioxide  will  result  in 
the  formation  of  more  of  the  gas.  It  will  be  noticed  that  heat  is 
absorbed  when  the  reaction  proceeds*  toward  the  right  and  evolved  when 
it  goes  in  the  opposite  direction;  and,  further,  that  for  every  100  grms. 
of  CaC03  decomposed  43741  cal.  of  heat  are  rendered  latent. 

If  we  examine  this  reaction  further  in  the  light  of  the  principle  of 
Le%  Chatelier.  we  are  enabled  to  predict  the  direction  in  which  the 
equilibrium  will-  be  shifted  by  any  external  change.  This  law  states 
that  when  any  external  influence  is  brought  to  bear  on  a  system  in 
equilibrium  so  as  to  cause  a  change  in  that  equilibrium  the  direction  of 
the  change  will  always  be  such  as  to  minimize  the  effect  of  the  external 
influence"  Consequently,  if  we  raise  the  temperature,  the  reaction  will 
proceed  in  a  direction  so  as  to  absorb  heat.  If  we  attempt  to  increase 
the  pressure  of  carbon  dioxide,  this  gas  will  be  absorbed,  etc. 

The  decomposition  of  calcium  carbonate  is  greatly  accelerated  by  the 
pas-age  of  a  current  of  air  or  steam  through  the  kiln  so  that  a  much 
lower  temperature  can  be  used  in  burning  than  would  otherwise  be  the 
case.  It  will  be  noticed  from  the  table  that  at  812°  C.  the  pressure  of 
carbon  dioxide  is  753  mm.  or  nearly  one  atmosphere.  Now,  if  lime- 
stone be  heated  to  this  temperature  in  a  kiln  with  no  draught  there  will 
be  very  little  decomposition.  The  carbonate  will  decompose,  giving  off 
carbon  dioxide  until  the  atmosphere  of  the  kiln  becomes  saturated  with 
this  gas  or  until  the  partial  pressure  of  the  gas  is  equal  to  the  dissocia- 
tion pressure  of  the  calcium  carbonate,  when  the  reaction  will  cease 
until  some  of  the  carbon  dioxide  is  removed  and  the  partial  pressure  of 
the  gas  is  thus  reduced.  If,  on  the  other  hand,  a  current  of  air  or  steam 
be  passed  through  the  kiln  heated  to  this  temperature,  the  carbon  dioxide 
will  be  carried  away  as  fast  as  it  is  formed,  and  the  partial  pressure  of 
this  gas  will  not  be  permitted  to  rise  to  a  point  where  it  prevents  the  dis- 
sociation of  the  calcium  carbonate.  At  a  temperature  somewhat  higher 
than  900°  C.  the  pressure  of  carbon  dioxide  is  greater  than  atmospheric 
pressure,  consequently  dissociation  will  go  on  rapidly  so  long  as  the 
gas  is  permitted  to  escape,  regardless  of  whether  or  not  there  is  a 
draught  through  the  kiln. 

The  dissociation  of  calcium  carbonate  may  be  compared  to  the  evap- 
oration of  water.  As  the  vapor  pressure  of  water  increases  with  the 
rise  in  temperature,  so  does  the  dissociation  pressure  of  calcium  car- 
bonate. At  100°  the  vapor  pressure  of  water  is  equal  to  the  atmos- 
pheric pressure,  while  the  pressure  of  C02  from  CaCO,  is  equal  to  an 
atmosphere  at  about  900°.  If  a  flask  containing  a  few  cubic  centimeters 
of  water  be  heated  to  a  temperature  below  100°,  the  water  will  evaporate 
slowly;  whereas,  if  a  current  of  dry  air  be  drawn  through  it,  the  water 
will  evaporate  rapidlv,  just  as  it  would  in  an  open  dish  with  the  wind 
blowing  over  its  surface.     When  heated  to  100°  water  passes  off  rapidly 


22  STUDY   OF   SAND-LIME   BRICK. 

as  vapor,  regardless  of  the  kind  of  vessel  in  which  it  is  heated,  or  any 
other  condition,  save  the. rate  at  which  heat  is  supplied.  The  rate  of 
evaporation  is  dependent  on  the  ability  of  the  vapor  to  get  away ;  under 
the  conditions  first  described,  it  could  get  away  only  by  diffusion 
through  the  air;  while  in  the  presence  of  the  current  of  air,  it  is 
carried  off.  In  the  burning  of  lime,  we  have  an  exactly  similar  phe- 
nomenon. At  900°  the  reaction  proceeds  rapidly,  dependent  only  on  the 
rate  at  which  heat  is  supplied.  This  temperature  corresponds  to  the 
boiling  point  in  a  liquid,  since  decomposition  proceeds  rapidly  only  so 
long  as  heat  is  supplied  and  the  gas  is  free  to  escape  into  the  atmos- 
phere. At  lower  temperatures,  on  the  other  hand,  the  decomposition 
proceeds  only  so  long  as  the  gases  resulting  from  the  decomposition  are 
removed  in  some  way,  and  their  pressure  is  kept  below  that  of  the 
carbon  dioxide  resulting  from  the  decomposition  of  the  calcium  car- 
bonate. 

Calcium  oxide,  when  treated  with  water,  reacts  according  to  the  equa- 
tion : 

CaO+H20=Ca   (OH)2+15,100  cal. 

It  will  be  seen  from  the  equation  that  this  reaction  proceeds  with 
the  evolution  of  heat,  and  that  the  amount  of  heat  evolved  is  one-third 
of  that  required  to  effect  the  decomposition  of  calcium  carbonate. 

The  ease  with  which  water  combines  with  calcium  oxide  is  influenced 
by  the  presence  of  impurities  and  by  the  temperature  at  which  the  lime 
was  burned.  Very  pure  lime,  burned  from  calcium  nitrate,  hydrates 
slowly,  while  lime  burned  from  pure  limestone,  hydrates  readily. 
Hydraulic  limestones  containing  much  clay  hydrate  slowly,  and  if  the 
quantity  of  clay  present  is  as  great  as  30  to  50  per  cent  it  does  not 
hydrate  at  all,  unless  first  finely  pulverized.  If  heated  to  temperatures 
higher  than  that  at  which  the  dissociation  pressure  is  equal  to  the 
atmospheric  pressure,  limes' may  be  overburned.  When  heated  to  1600°, 
pure  calcium  oxide  forms  a  white  porcelain-like  mass  which  may  be 
hydrated  only  with  difficulty.  Limestones  containing  clay  and  silica 
are  much  more  easily  overburned  than  pure  limestones,  owing  to  the 
formation  of  silicates,  aluminates,  etc.  It  is  very  difficult  to  burn  good 
lime  from  magnesium  limestones,  owing  to  the  fact  that  a  much  higher 
temperature  is  required  to  decompose  the  calcium  carbonate  than  the 
magnesium  carbonate,  and  consequently  great  care  is  required  to  pre- 
vent the  magnesium  oxide  from  fritting,  and  at  the  same  time  to  expel- 
completely  the  carbon  dioxide  from  the  calcium  carbonate. 

On  hydration,  calcium  oxide  undergoes  a  change  in  density  from 
about  3.13  to  2.078,  and,  consequently,  a  change  in  volume.  The 
increase  in  the  apparent  volume  of  the  oxide  on  changing  to  the  hydrate 
is  about  3y2  when  just  the  right  amount  of  water  is  used.  The  increase 
varies  quite  considerably,  however,  according  to  the  method  used  in 
slaking.  This  expansion  on  hydration  explains  the  injurious  effect  of 
lumps  of  unslaked  lime  in  bricks,  mortar,  cement,  etc. 


CONSTITUENTS   OF   SAND-LIMB  BRICKS.  23 

Both  caustic  and   hydrated   lime  combine  quite  readily   with  carbon 
dioxide   in  the  proportion-  shown  by  the  equations, 
CaO+C02==CaC08+43,741  cal. 
Ca  (OH)2+CO2=CaCOs+H2O+28>640  cal. 

It  will  be  noted  that  when  carbon  dioxide  combines  with  calcium 
oxide  or  with  slaked  lime  heat  is  evolved.  The  partial  pressure  of 
carbon  dioxide  in  the  atmosphere  is  only  0.23  mm.,  consequently,  caustic 
lime,  when  slightly  heated,  will  not  take  up  C02  from  the  air.  If, 
however,  lime  be  heated  in  a  crucible  and  C02  be  conducted  over  it 
so  that  the  pressure  of  C02  is  equal  to  an  atmosphere,  combination  takes 
place  quite  readily,  and  the  lime  glows  until  the  reaction  is  completed. 

All  these  facts  show  that  lime  is  a  powerful  base,  combining  easily 
with  even  the  weakest  acids.  Silica  or  silicic  acid  and  lime  combine  not 
only  at  high  temperatures,  but  also  at  temperatures  comparatively  low. 
When  a  mixture  of  lime  and  finely  divided  silica  is  subjected  to  steam 
pressure,  combination  takes  place  and  a  hard  artificial  sandstone  is 
produced.  This  is  the  reaction  on  which  the  sand-lime  brick  industry 
is  based. 


24 


THE   RAW    MATERIALS    OF    THE    SAND-LIME 
BRICK  INDUSTRY. 


The  materials  used  in  the  manufacture  of  sand-lime  bricks  are  clean 
quartz  sand,  or  other  material  rich  in  silica,  and  lime,  with  the  prefer- 
ence in  favor  of  calcium  lime  rather  than  the  magnesian  variety.  Bricks 
apparently  good  at  the  time  of  manufacture  can  be  made  from  impure 
sands,  but  such  bricks  will  not  withstand  the  action  of  the  weather  so 
well  as  those  in  which  purer  sands  are  used. 

Sand. 

occurrences  and  origin. 

Sand  is  one  of  the  products  resulting  from  the  disintegration  of  rocks. 
It  may,  therefore,  be  composed  of  many  different  kinds  of  minerals  and 
consequently  vary  widely  in  chemical  composition.  With  reference  to 
the  size  of  its  particles,  sand  lies  between  the  clays,  on  the  one  hand, 
and  the  gravels,  on  the  other.  Materials  passing  screens  all  the  way 
from  5  to  100  mesh  may  properly  be  spoken  of  as  sands.  In  some  sands 
there  is  gradation  of  sizes,  while  in  others  the  grains  are  all  of  nearly 
the  same  size.  Furthermore,  sand  may  vary  widely  in  the  character  of 
the  grains,  some  of  them  being  round,  while  others  are  sharp. 

Most  of  our  soils,  sands,  sedimentary  rocks,  etc.,  were  formed  origi- 
nally by  the  disintegration  of  igneous  rocks.  Where  the  molten  material 
or  lava  cooled  rapidly  it  produced  obsidians  or  glasses  of  uniform 
composition,  but  not  corresponding  to  any  definite  chemical  formula. 
Where,  on  the  other  hand,  the  mass  of  material  cooled  slowly  crystalliza- 
tion took  place,  several  constituents  separated  as  minerals,  and  compar- 
atively coarse-grained  rocks — of  which  granite  is  a  type — resulted.  In 
granite  are  distinct  grains  of  quartz,  mica,  hornblende,  feldspar,  and 
several  other  minerals.  When  rocks  of  this  kind  are  exposed  to  the 
action  of  the  weather,  the  softer,  and  less  resistant  constituents  crumble 
away  first.  Quartz,  which  is  the  most  resistant  of  all  the  constituents, 
is  left  behind,  .and  collects  in  stream  beds  as  sand. 

Feldspar  is  also  found  in  some  sands,  soils,  and  clays,  but  being  less 
resistant  than  quartz,  it  is  less  abundant  than  this  mineral  in  the  resi- 
dues left  by  weathering.     Feldspar  sands,  limestone  sands,  chalks,  marls, 


KAW    MATERIALS    OF    SAND-LIME    BRICKS. 


25 


etc.,  are  entirely  unsuited  to  take  the  place  of  ordinary  .-and  in  the 
manufacture  of  sand-lime  bricks.  In  its  generally  accepted  sense,  the 
term  "sand"  signifies  quartz  sand,  and  it  is  quite  essential  that  sand 
should  be  of  this  character  when  it  is  to  be  used  in  the  manufacture  of 
sand-lime  bricks,  although,  for  some  other  purposes,  such  as  for  mortar, 
concrete,  etc.,  feldspathic  sands  or  sands  of  any  other  character  will  do 
quite  well. 

Sands  may  be  variously  classified  according  to  their  modes  of  occur- 
rence, their  origin,  etc.,  into  (1)  those  which  have  been  shifted  about 
and  sorted  by  the  winds,  usually  spoken  of  as  bank  sands;  (2)  those 
transported  by  running  streams,  called  river  sands;  and  (3)  those 
occurring  on  lake  and  ocean  shores,  known  as  lake  and  sea  sands.  Beds 
of  sand  which  have  been  formed  by  the  grinding  action  of  glaciers  and 
the  sorting  action  of  glacial  streams  are  also  met  with  occasionally. 
These  are  called  glacial  sands. 

Sands  from  all  these  sources  are  used  in  the  sand-lime  brick  industry, 
as  are  also,  in  several  instances,  silica-containing  materials  not  prop- 
erly called  sands.  In  the  report  on  the  Mineral  Eesources1  of  the 
United  States  for  1908,  there  were  74  plants  reported  as  producing 
sand-lime  bricks.  For  the  purpose  of  securing  data  on  various  phases 
of  the  manufacture  of  these  bricks,  circular  letters  were  mailed  to  each 
of  the  plants.  The  information  obtained  in  response  to  a  question 
as  to  the  kind  of  sand  used  is  shown  in  the  following  table : 


Table  5 — Kind  of  sand  used  in  the  manufacture  of  sand-lime  bricks  in 

the  United  States. 

Number  of  plants  using— 


Bank 
sand. 

River 
sand. 

Lake 
sand. 

Sea 
sand. 

Crushed 
stone. 

Weathered 
stone. 

Ore 
tailings. 

Total 
reporting. 

29 

16 

3 

2 

G 

1 

1 

56 

The  principal  materials  utilized  as  sand  in  the  sand-lime  brick  indus- 
try in  this  country  are  bank  and  river  sands,  and  crushed  stone.  The 
use  of  tailings  from  copper  ore  is  quite  unusual,  as  is  also  the  use  of 
crushed  granite,  which  was  reported  by  one  firm.  However,  these  inci- 
dents merely  show  that,  so  far' as  the  ability  to  make  good  brick  is 
concerned,  the  origin  of  the  material  is  utterly  insignificant  so  long  as 
it  possesses  the  proper  chemical  composition. 

IMPURITIES  IN  SAND. 

The  ordinary  impurities  found  in  quartz  sand  are  silicates  such  as 
occur  associated  with  quartz  in  granite  and  other  rocks,  and  their  decom- 
position products.    Clay,  or  kaolin,  is  one  of  the  most  important  of  these 


1  Mineral  Resources,  U.  S.  for  1908,  0*.  8.  Geological  Survey,  1909,  p.  517. 


26  STUDY   OF    SAND-LIME   BRICK. 

decomposition  products.  It  results  from  the  breaking  down  of  felds- 
pathic  minerals,  of  which  potassium  feldspar,  or  orthoclase,  is  typical. 
This  mineral  has  the  chemical  formula : 

KAlSi368  or  H2O.Al203.6Si02. 
and  the  following  composition: 

Silica    (Si02)     64.68  per  cent 

Alumina    ( A1203)    18.43  per  cent 

Potash   (K20)    16.89  per  cent 

When  exposed  to  the  action  of  the  weather,  orthoclase  decomposes 
according  to  the  following  reaction: 

K2O.Al203.6Si02+2H20+C02=Al203.2Si02+4Si02+K2C03. 
The  silica  and  potassium  carbonate  resulting  from  this  action  may 
be  carried  away  in  solution,  leaving  the  substance  Al203.2Si02.2H20, 
which  is  present  in  all  clays,  and  which,  when  pure,  is  called  kaolin, 
kaolinite,  or  clay  substance.  Clay  substance  is  an  almost  ever  present 
impurity  in  sands,  as  is  also  ferric  oxide,  one  of  the  decomposition 
products  of  iron  bearing  minerals  which  are  nearly  always  present  in 
igneous  rocks. 

Lime. 

impurities. 

The  lime  intended  for  use  in  the  manufacture  of  sand-lime  bricks 
should  be  of  a  high  grade.  It  should,  therefore,  be  burned  from  good 
materials  in  the  best  manner  for  producing  good  lime. 

The  raw  materials  from  which  limes  are  burned  are  limestone  of 
various  degrees  .of  purity,  and  marble.  The  impurities  found  in  lime- 
stone and,  consequently,  in  the  burned  lime,  are  ferric  oxide,  alumina, 
silica,  and  occasionally  traces  of  other  substances.  When  present  in 
the  limestone,  these  materials  usually  combine  with  the  lime  during 
burning,  and  so  render  a  part  of  it  inactive.  This  is  especially  true 
when  heating  is  carried  much  beyond  the  temperature  where  decomposi- 
tion is  complete. 

Magnesia  is  usually  present  in  commercial  limes  to  some  extent.  This 
oxide  is  quite  similar  to  the  oxide  of  calcium  and  when  the  lime  is 
intended  for  use  in  mortars,  plaster,  etc.,  is  not  considered  particularly 
objectionable.  It  is  much  less  basic,  however,  than  calcium  oxide,  and 
consequently  it  reacts  with  silica  much  less  readily  than  pure  lime, 
when  used  in  the  manufacture  of  sand-lime  bricks. 
•  Limes  have  been  variously  classified  as  white  and  gray;  hot  and  cool; 
fat  and  lean;  quick  and  slow.  These  terms  are  intended  to  distinguish 
between  limes  relatively  pure  on  the  one  hand,  and  those  containing 
considerable  clay  or  magnesia  on  the  other.  They  are  all  used  in  a 
very  general  way,  however,  so  that  when  a  lime  of  a  particular  grade 
is  desired  for  a  special  purpose,  it  is  necessary  to  specify  more  definitely 
the  limits  beyond  which  impurities  may  not  go. 


RA.W    MATERIALS   OF    SAND-LIME    BRICKS.  27 

BURNING  OE  LIME. 

in  burning  lime  it  is  necessary  in  some  way  to  heat  the  stone  to  a 
temperature  of  900°  or  1000°  and  maintain  this  temperature  for  a 
sufficient  length  of  time  to  allow  the  chemical  reaction,  which  is  started 
by  the  heat,  to  run  to  completion.  The  processes  used  in  burning  lime 
are  numerous.  Lime  was  formerly  burned  by  heaping  up  piles  of  logs 
and  limestone  and  setting  fire  to  the  pile.  Today,  numerous  types  of 
kilns  are  used,  which  are  constructed  so  as  to  make  use  of  coal,  wood, 
gas,  etc.,  as  fuel. 

The  kiln  in  most  general  use  is  the  shaft  kiln  which  is  nothing  more 
than  a  cylindrical  shaft,  into  the  top  of  which  the  fuel  and  stone  are 
dumped,  to  pass  downward  as  the  fuel  is  consumed.  The  ashes  and 
burned  lime  are  removed  from  the  bottom.  Air  enters  at  the  bottom, 
and,  becoming  heated,  passes  upward  through  the  kiln,  thus  furnishing 
the  draught.  In  some  cases  a  jet  of  steam,  and  in  others  a  forced 
draught  is  used  to  aid  the  decomposition  of  the  limestone.  Gas  is  used 
as  fuel  in  some  plants  in  this  country,  partly  because  of  its  cheapness, 
and  partly  because  of  the  greater  ease  with  which  the  heat  produced  by 
its  combustion  can  be  so  distributed  through  the  kiln  as  to  prevent  over- 
burning.  Plate  II  is  a  cross  section  of  a  semi-gas  fired  kiln  designed 
by  Theodore  Gerhard.  Its  description  may  be  found  in  the  Tonin- 
dustrie  Zeitung,  No.  11,  page  103,  and  No.  14,  page  144.  The  advan- 
tage of  this  kiln  over  the  ordinary  gas-fired  kiln  is  that  the  sensible 
heat  of  the  gas  is  not  lost. 

COST   OF  BURNING   LIME. 

From  the  reaction  given  in  a  previous  section  of  this  article,  it  will 
be  seen  that  43741  cal.  of  heat  are  actually  used  (absorbed  or  rendered 
latent)  by  every  100  grams  of  calcium  carbonate  decomposed,  or  for 
every  56  grams  of  calcium  oxide  formed.  With  this  as  a  basis,  the 
amount  of  heat  necessary  for  the  formation  of  one  ton  of  lime  from 
limestone  can  be  calculated.     The  heat  of  formation  of  one  gram  of 

43741 

CaO   from    CaC03   is   from   the   above  equation   =  781.1   cal. 

56 
9 
This  is  equivalent  to  781.1  X-  =1405  B.t.u.  per  lb. 

5 

The  B.t.u.  value  of  a  pound  of  average  Illinois  coal  is  11,000,  so  that, 

to  find  the  weight  of  coal  actually  required  to  produce  the  heat  necessary 

to  make  a  ton  of  lime,  we  have  only  to  divide  the  number  of  B.t.u. 

needed   by   the   available   heat   content   of   the   fuel,    or,    in   this    case, 

1405X2000 

,  which  gives  0.1277  ton,  or  255.6  pounds.     This  item  in  the 

11000 
fuel  composition  is  fixed,  and  cannot  be  reduced  by  any  process  whatso- 
ever.    Assuming  a  price  of  $3.00  per  ton  for  coal,  the  "cost  of  the  heat 
actually  used  would  be  38  cents. 


28  STUDY   OF    SAND-LIME   BRICK. 

In  addition  to  the  heat  used  to  decompose  the  carbonate,  there  are 
certain  unavoidable  losses  in  heat  due  to  the  fact  that  all  products  leave 
the  kiln  at  a  temperature  higher  than  that  at  which  they  entered.  The 
lime  rock  enters  at  an  average  temperature  of  perhaps  20° C.  and  the 
lime  leaves  it  at  various  temperatures,  depending  upon  the  construction 
of  the  kiln.  The  same  may  be  said  of  the  fuel,  of  the  carbon  dioxide 
resulting  from  its  combustion  and  from  the  decomposing  carbonate,  and 
of  the  nitrogen  and  oxygen  of  the  air  used  in  burning.  If  steam  is 
used  to  help  create  a  draft  through  the  kiln,  this  too  must  be  taken 
into  account  in  the  heat  balance.  Knowing  the  temperatures  at  which 
the  various  materials  enter  the  kiln,  the  temperatures  at  which  the 
products  leave  it  and  the  heat  capacities  of  the  various  substances,  it  is 
easy  to  calculate  the  total  amount  of  heat  employed  in  producing  one 
ton  of  lime,  and  the  cost  of  the  fuel  required  to  produce  this  heat.  It 
may  be  said  that  any  device  which  has  the  effect  of  lowering  the  tempera- 
ture of  the  outgoing  products  will  effect  a  saving  in  the  cost  of  fuel. 

MARKET   GRADES   OF   LIME. 

Caustic  lime  is  usually  shipped  in  the  lump  just  as  it  comes  from 
the  kiln,  although  for  some  industries,  as,  for  example,  plate  glass 
manufacturing,  it  is  ground.  When  shipped  as  "lump"  it  may  be 
either  in  bulk  or  barreled.  When  shipped  in  bulk  it  is  wheeled  from 
the  kiln  into  tight  box  cars  while  still  warm;  the  cars  are  closed,  and 
sent  directly  to  the  consumer,  who  usually  has  provided  his  plant  with 
an  air-tight  bin  large  enough  to  hold  a  supply  of  lime  sufficient  to  last 
for  some  time.  It  is  in  this  condition  that  lime  is  usually  shipped  for 
the  sand-lime  brick  industry.  When  barreled,  the  cost  is  increased  about 
10  cents  per  hundred  pounds.  The  barrels  are  filled  and  headed  while 
the  lime  is  still  warm  enough  to  prevent  the  combination  with  it  of 
carbon  dioxide  from  the  atmosphere.  When  lime  is  to  be  ground,  it 
is  cooled  and  passed  through  a  crusher  which  reduces  it  to  about  80 
mesh.  It  is  claimed  that  crushed  lime  keeps  better  than  lump  lime, 
and  that  it  is,  moreover,  easily  hydrated  when  ready  to  be  used.  In 
this  condition  it  may  also  be  shipped  in  special,  moisture  proof  bags 
more  conveniently  than  when  in  the  lump  condition. 

Another  form  in  which  lime  is  now  being  marketed  quite  extensively 
is  the  hydrate,  which  goes  under  the  trade  name  of  "hydrated"  or 
"prepared"  lime.  This  is  a  very  convenient  form  in  which  to  handle 
the  material ;  but  because  it  weighs  about  one-third  more  than  the  same 
amount  of  caustic  lime,  it  is  more  expensive  to  transport. 

There  are  several  processes  in  use  for  preparing  hydrated  lime.  In 
one,  a  closed  cylindrical  shell  of  boiler  plate  steel  is  mounted  so  that 
it  may  be  rotated.  A  charge  of  caustic  lime  with  the  proper  amount 
of  water  to  hydrate  it  are  dumped  into  the  cylinder  through  a  manhole. 
When  closed,  the  cylinder  is  rotated  and  hydration  begins.  A  gage 
enables  the  operator  to  watch  the  progress  of  the  reaction  within.  When 
hydration  is  complete,  a  valve  is  opened  and  the  excess  water  passes  off 
as  steam,  leaving  a  dry  and  completely  hydrated  lime. 


ILLINOIS  SPATE  GEOLOGICAL  SURVEY. 


Bull.  No.  18,   Plate   i  I 


Cross-section  of  semi-gas  fired  kiln,  designed  by  Theo.  Gerhard. 


RAW   MATERIALS   OF    SAND-LIME    BRICKS.  29 

Iii  another  process  a  steel  shell,  open  at  both  ends,  is  mounted  like  a 
rotary  cement  kiln.  The  quick  lime  and  water  are  fed  in  at  the  upper 
end.  As  they  pass  downward  together,  hydration  takes  place,  while  a 
jet  of  superheated  steam,  blown  in  at  the  lower  end,  drives  out  any 
excess  water  that  may  have  found  its  way  down  with  the  lime. 

Numerous  other  processes  for  the  hydration  of  lime  have  been  pat- 
ented, and  some  of  them  are  in  use.  In  these  the  water  is  added  in 
small  amounts  and  the  hydrated  lime  as  fast  as  it  forms  is  removed  my 
moans  of  screens.  It  is  evident  that  the  dry  slaking  method  must  be 
used  in  order  to  prepare  a  dry  hydrate  cheaply;  but  by  any  of  these 
processes,  except  the  first  one  mentioned,  where  the  hydration  is  done 
by  steam  under  pressure,  it  does  not  seem  improbable  that  some  parti- 
cles of  caustic  lime  will  pass  through  the  screens  and  be  present  in  the 
finished  product.  Such  a  lime,  if  used  in  the  manufacture  of  sand-lime 
bricks,  might  give  serious  trouble  unless  the  mixture  is  well  siloed 
before  pressing. 

METHODS    OF    TESTING    LIME. 

In  order  to  determine  the  quality  of  any  lot  of  lime,  resource  must 
be  had  to  chemical  analysis,  by  which  the  exact  amounts  of  calcium 
oxide,  magnesium  oxide,  clay,  unburned  stone,  etc.,  present  in  the 
sample,  may  be  detected.  Chemical  analysis  alone,  on  the  other  hand, 
will  not  distinguish  between  a  properly  burned  lime  and  one  which  is 
overburned,  nor  between  quick  hydrating  limes  and  slow  hydrating 
varieties.  Since  it  is  very  essential  that  the  lime  used  in  the  sand-lime 
brick  industry  should  hydrate  readily  and  also  that  it  be  of  the  high 
calcium  type,  it  is  important  to  be  able  to  determine  these  qualities 
rapidly  and  accurately. 

The  heat  of  hydration  of  one  gram  of  pure  calcium  lime  (CaO)  is 
269.6  calories.  The  heat  of  hydration  of  one  gram  of  magnesium  lime 
(MgO)  is,  on  the  other  hand,  only  135  calories,  or  about  one-half  that 
of  pure  calcium  oxide.  Again,  it  has  been  shown  that  when  lime  has 
been  heated  to  a  high  temperature  (1100°-1300°)  it  slakes  very  slowly, 
especially  when  considerable  clay  is  present.  From  these  considerations 
it  follows  that  a  simple  determination  of  the  amount  of  heat  given  off 
on  hydrating,  and  the  time  required,  after  the  addition  of  water,  to 
reach  a  maximum  temperature,  is  sufficient  to  distinguish  between  a 
properly  burned  high  calcium  lime  and  all  others.  For  this  determina- 
tion only  very  simple  apparatus  is  required.  It  is  necessary  to  have 
some  containing  vessel  of  suitable  size,  preferably  with  polished  sides 
and  covered  with  felt,  wool,  or  some  good  non-conductor  of  heat,  and  a 
thermometer.  Furthermore,  some  means  of  weighing  out  samples  must 
be  at  hand.  The  determination  is  made  by 'filling  the  vessel  to  be  used 
as  a  calorimeter  with  some  convenient  quantity  of  water  at  a  known 
temperature.  A  weighed  quantity  of  lime  is  then  added  and  the  mixture 
is  -tirred.  the  temperature  being  noted  at  minute  intervals.  If  the 
quantity  of  water  used  is  100  times  the  weight  of  the  lime,  the  maximum 
rise  in  temperature  should  be  about  2.5°  Centigrade  or  4.5°  Fahrenheit 


30 


STUDY   OF    SAND-LIME   BRICK. 


for  material  consisting  of  pure  CaO.  Limes  well  suited  to  the  sand- 
lime  brick  industry  will  reach  the  maximum  temperature  quickly.  When 
comparing  various  limes  it  is  well  to  plot  thermometer  readings  against 


gH8Hg 

Commercial  Lime  No.l. 
Commerc/ol  L/me  No.? 

< 

■/** 

yoooo 

oo-o  Pure  Ca/cium   Oxide 

v. 

^^ 

^fr^SHgHS 

H» 

3 

^r^ 

1 

[Zas 

/S  20  2S  JO 

.  Time  in  Minute's 


45 


Fig.  2.     Curves  showing  rise  of  temperature   in  the  hydration  of  samples 

of  lime. 


time.  The  following  curves,  which  are  the  records  of  tests  on  a  pure 
calcium  oxide  and  two  commercial  limes  (Fig.  2),  show  how  this  may 
be  done. 


31 


TECHNIQUE  OF  THE  MANUFACTURE   OF 
SAND-LIME  BRICKS. 


Processes  for  Preparing  Mixtures. 

The  first  step  in  the  manufacture  of  sand-lime  bricks  is  the  mixing 
of  the  sand  and  lime,  and  it  is  in  this  that  the  various  processes  differ. 
The  subsequent  steps — the  pressing  or  molding  and  hardening  of  the 
mixture — are  practically  the  same  in  all  plants,  except  as  to  kind  of 
machinery  used. 

According  to  the  Keramisches  Jahrbuch,  1909,  there  were  in  use  in 
Germany  in  1908  five  processes  for  preparing  the  mixture  used 'in  the 
sand-lime  brick  industry.     These  were  known  as : 

The  pure  hydrate  methods,  in  which  (1)  burned  lime  is  slaked  (in 
any  way)  without  the  addition  of  sand,  pulverized,  and  finally  mixed 
with  sand  and  pressed; 

Mixed  methods,  in  which  (2)  burned  lime  is  slaked  with  a  part  of 
the  sand,  then  mixed  with  the  remainder  and  pressed;  or  (3)  burned 
lime  is  partly  pulverized  and  mixed  with  a  part  of  the  sand,  and  then 
placed  in  the  silo  for  a  while,  after  which  it  is  mixed  with  the  remainder 
of  the  sand  and  pressed;  and, 

Caustic  lime  methods,  in  which  (4)  the  entire  quantity  of  sand  is 
mixed  with  the  pulverized  caustic  lime  in  a  mixing  machine,  and  then 
is  cured  in  a  silo  and  pressed;  or  (5)  pulverized  caustic  lime  is  mixed 
with  all  the  sand  in  a  slaking  machine  until  a  good  mixture  is  obtained, 
when  it  is  pressed. 

Complete  information  as  to  the  extent  to  which  these  various  methods 
are  used  in  Germany  was  not  given.  The  results  of  a  circular  letter 
sent  out  by  the  Verein  der  Kalksandsteinfabriken  relative  to  the  matter 
are  given  in  the  following  table : 


Table  6 — Xumber  of  plants  using  various  processes  of  preparing  mix- 
tures for  sand-lime  bricks. 


Method. 

Number  of  plants. 

No.  (1) 

f>2 

21 

1 

.37 

No.  (2) 

No.  (3) 

No.  (i) 

No.  (5) . 

13 

32 


STUDY   OF    SAND-LIME   BRICK. 


In  order  to  get  an  idea  of  the  prevailing  processes  in  the  United 
States,  the  following  statement  was  mailed  to  the  131  companies, 
reported  as  being  manufacturers  of  sand-lime  bricks,  with  the  request 
that  each  check  the  number  which  covers  liiS  process : 

1.  Lime  is  slaked  before  being  mixed  with  any  part  of  the  sand. 
Caustic  lime  is  mixed  with  a  part  of  the  sand  and  slaked. 
It  is  then  mixed  with  the  remainder  of  the  sand  and  pressed. 
Caustic  lime  is  finely  pulverized  and  mixed  with  a  part  of 
the  sand  and  sufficient  water  to  completely  hydrate  it.  It  is 
then  stored  for  a  time  in  a  silo,  after  which  it  is  mixed  with 
the  remainder  of  the  sand  and  pressed. 

Caustic  lime  is  finely  pulverized  and  mixed  with  all  the  sand 
and  sufficient  water  to  insure  complete  hydration.  It  is  then 
stored  in  a  silo  for  a  time  and  pressed. 

5.  Caustic  lime  is  finely  pulverized  and  mixed  with  all  the.  sand. 
The  mixture  is  then  passed  through  a  machine  in  which  the 
lime  is  completely  hydrated,  after  which  it  is  pressed. 

6.  The  caustic  lime  and  a  part  of  the  dried  sand  are  ground 
together.  This  mixture  is  then  mixed  with  the  remainder  of 
the  sand  and  sufficient  water  added  to  insure  complete  hydra- 

.    tion  of  the  lime.     The  mixture  is  then  siloed  for  a  day  and 
pressed. 
The  results  of  this  inquiry  are  shown  in  the  table  following: 


2. 


3. 


4. 


Table  7 — Processes  employed  in  preparing  mixtures  for  the  manufac- 
ture of  sand-lime  bricks  in  the   United  States. 


• 

Process  No.  3. 

Total  reporting. 

1. 

2. 

3. 

4. 

5. 

6. 

Number  of  plants  using 

29 

0 

3 

12 

2 

lo 

61 

In  this  country,  as  in  Germany,  more  plants  use  the  slaked-lime 
method  than  any  other  single  one.  However,  if  we  combine  4,  5,  and  6 
(the  caustic  lime  processes),  the  balance  is  in  favor  of  this  practice. 
The  prevalance  of  these  two  processes  in  this  country  makes  it  seem 
desirable  to  discuss  them  somewhat  more  at  length.  Accordingly,  under 
the  first  heading  (hydrated  lime  methods)  will  be  considered  all  those 
processes,  in  which  the  lime  is  hydrated  before  being  mixed  with  the 
sand,  and  under  the  second  heading  (caustic  lime  methods)  those  in 
which  the  sand  is  mixed  with  the  lime  in  the  caustic  condition. 


THE   HYDRATED   LIME   METHODS. 


Where  process  No.  1  is  used  the  question  as  to  the  best  method  of 
slaking  the  lime  arises.     There  have  been  many  patents  issued  for  spe- 


TECHNIQUE   OF    MANUFACTURE .  33 

cial  methods  of  procedure  in  carrying  out  this  operation,  but  they  all 
fall  into  one  of  two  classes,  namely:  (1)  the  wet,  and  (2)  the  dry 
slaking  process. 

In  the  wet  slaking  process  water  enough  is  added  to  the  lime  to  form 
a  thick  paste  or  putty.  Machines  of  various  kinds  are  in  use  for  stirring 
the  lime  so  as  to  continually  expose  fresh  surfaces".  With  properly 
burned  fat  limes  the  slaking  takes  place  easily,  and,  if  the  proper  amount 
of  the  water  has  been  added,  the  lime  swells  up  to  a  volume  of  about 
31/}  times  that  of  the  original  caustic  lime.  In  this  condition  it  is 
mixed  with  the  sand  and  pressed. 

It  is  claimed  by  the  advocates  of  this  method  that  all  of  the  lime  is 
completely  hydrated  and  that  each  molecule  of  calcium  oxide  takes  up, 
either  chemically'  or  otherwise,  several  times  as  much  water  as  that 
required  by  the  chemical  formula  of  the  hydrate.  This  phenomenon 
appears  to  take  place  only  when  the  quantity  of  water  added  is  just 
sufficient  to  form  a  thick  paste.  If  less  be  added  the  temperature  rises 
high  enough  to  expel  the  water,  which  might  otherwise  be  retained, 
while  if  too  much  be  added  the  temperature  is  kept  down  to  a  point 
where  the  oxide  appears  to  be  unable  to  take  up  more  water  than  that 
required  by  the  chemical  formula.  This  increase  in  volume  and  plas- 
ticity enables  the  lime  to  envelope  the  sand  grains  more  completely  than 
is  the  case  when  dry  slaking  method  is  used.  On  the  other  hand,  the 
mixing  is  more  expensive  in  that  more  power  is  required  and  the  process 
cannot  be  completed  so  quickly.  Again,  there  is  no  chance  to  screen 
lime  slaked  by  the  wet  method,  consequently  lumps  of  unburned  or  over- 
burned  lime  are  apt  to  get  into  the  bricks,  thus  injuring  their  quality. 

In  the  dry  slaking  process  just  enough  water  is  added  to  give  a  dry 
product.  By  this  method  it  is  possible  to  screen  out  lumps  of  unslaked 
or  improperly  burned  lime.  Mixing  is  also  easily  accomplished,  but  it 
is  doubtful  whether  the  sand  particles  are  as  completely  surrounded  by 
the  lime  in  this  method  as  in  the  wet  slaking  process.  In  this  method, 
however,  there  is  a  possibility  of  fine  particles  of  caustic  lime  passing 
through  the  screen  so  that  unless  the  mixture  is  well  siloed  before  press- 
ing, trouble  is  liable  to  occur  due  to  subsequent  hydration  in  the  hard- 
ening c}dinder. 

THE    CAUSTIC    LIME    METHODS. 

There  are  several  methods  of  procedure  employed  in  the  caustic  lime 
processes.  According  to  one  method  pulverized  caustic  lime  is  mixed 
with  the  sand,  or  a  part  of  it,  and  enough  water  is  then  added  to  slake 
the  lime  and  give  the  mixture  the  proper  consistency  for  the  press.  The 
mixture  may  pass  directly  to  the  press  as  in  process  No.  5,  or  be  stored 
in  a  silo  to  cure. 

Process  Xo.  6  is  that  of  the  American  Sand-Lime  Brick  Machinery 
Company.  It  is  a  caustic  lime  process  in  which  a  part  of  the  dried 
sand  is  ground  with  the  caustic  lime  to  a  fine  flour,  which  is  then  mixed 
with  the  remainder  of  the  sand,  wet  to  the  proper  consistency,  and  sent 

—3  G 


34 


STUDY    OF    SAND-LIME    BRICK. 


to  the  silo  until  cured.  It  is  evident  that  by  grinding  the  lime  with  a 
part  of  the  sand  perfect  mixing  is  effected,  and  at  the  same  time  each 
particle  of  sand  is  surrounded  with  a  film  of  lime.  When  this  ground 
mass  is  later  mixed  with  the  remainder  of  the  sand,  the  tendency  to 
ball  up  and  form  lumps  is  avoided.  Again,  it  is  claimed  that  by  grind- 
ing the  lime  and  sand  together  the  manufacturer  is  practically  assured 
that  all  the  lime  that  remains  in  the  mixture  will  be  reduced  to  a  size 
so  small  that  no  damage  will  result  from  its  being  incorporated  in  the 
brick. 

It  will  be  evident  from  what  has  been  said  that  in  the  caustic  methods 
wet  sands  may  be  worked  without  much  inconvenience,  as  the  moisture 
in  the  sand  will  be  taken  up  by  the  caustic  lime.  When  this  procedure 
is  adopted,  however,  none  but  the  best  quick  slaking  limes  should  be 
used,  for  if  magnesian  limes  are  used,  even  if  siloed  for  24  hours,  there 
is  a  possibility  of  improper  hydration  in  the  mixture  and  consequent 
swelling  and  rupture  of  the  bricks  while  in  the  hardening  cylinder. 

PREPARATION    OF    THE    SAND. 

It  is  generally  believed  that  an  assortment  of  various  sizes  of  sand  is 
advantageous  in  the  manufacture  of  sand-lime  bricks.  In  many  locali- 
ties sands  occur  in  which  the  proper  proportion  of  fine  and  coarse  mate- 
rial is  already  present,  and  in  others  access  may  be  had  to  several  banks 
some  of  which  are  fine  and  others  coarse.  Where  such  is  not  the  case, 
however,  the  practice  of  grinding  a  part  or  all  of  the  sand  is  commonly 
resorted  to.  The  following  table  is  given  to  show  to  what  extent  sand 
grinding  is  practiced  in  the  United  States: 

Table  8 — Practice  in  regard  to  grinding  sand  for  sand-lime  oricks  in 

the   United  States. 


Proportion  of  sand  ground. 

Total  reporting. 

None. 

All. 

Some. 

ft. 

ft. 

i 

4  • 

i 

5- 

1  < 

iV 

Number  of  plants 

29 

10 

10 

4 

3 

3 

1 

1 

2 

63 

The  question  of  fineness  of  sand  used  in  the  manufacture  of  brick  is 
one  that  has  received  considerable  attention  both  in  this  country  and 
abroad.  Some  ten  years  ago  Professor  E.  Gasenapp1  of  the  Polytechnic 
Institution  at  Riga  published  a  paper  in  which  he  described  two  series 
of  tests,  in  one  of  which  he  used  a  high  calcium  lime  and  in  the  other 
a  dolomitic  lime.  He  employed  also  two  grades  of  sand,  one,  a  coarse 
sand  0.6  to  1.0  mm.  in  diameter,  and  the  other  a  fine  sand  0.2  to 
0.3  mm.  in  diameter.  One  sample  of  each  lot  of  sand  was  treated  with 
10  per  cent  of  lime  and  another  sample  with  20  per  cent  of  lime,  and 
each  mixture  was  subjected  to  high  and  low  steam  pressure.  The 
results  of  this  work  are  tabulated  as  follows : 


Tonindustrie  Zeitung,  vol.  24,  1900,  p.  1703  and  vol.  25,  1901,  p.  762. 


TECHNIQUE   OF   MANUFACTURE. 


35 


Table  9 — Scries  A — Analyses  of  briquettes  in  which  pure  lime  was  used. 
(Analyzed  after  exposure  of  eight  hours  in  steam  cylinder.) 


Mixture. 


a 

<2  s 

. 

gp, 

O 

Si 

o 

"3 

_g  a 

o 

CQ 

Eh 

5 

6.50 

10 

9.38 

5 

1G  .69 

10 

16.59 

5 

8.74 

10 

10.10 

5 

15.81 

10 

17.67 

B 

o  C 

>>g 

o 

gq 

8 -a 

22 

o 

GQ 

90  parts  coarse  sand;  10  parts  lime 

Same  as  No.  1 

80  parts  coarse  sand;  20  parts  lime. 

Same  as  No.  3 

90  parts  fine  sand;  10  parts  lime. . . 

Same  as  No.  5 

80  parts  fine  sand;  20  parts  lime. . 
Same  as  No.  7 


1.67 
1.24 
7.16 
6.05 
0.85 
0.58 
4.23 
0.98 


0.42 


0.29 
0.31 
0.56 
0.31 
0.65 


3.45 

0.88 

0.43 

2.54 

2.96 

3.33 

4.77 

2.78 

0.59 

3.02 

4.60 

2.75 

3  .75 

1.79 

3.06 

2.23 

2.55 

7.58 

5.21 

3.90 

3.41 

3.13 

3.59 

11.14 

89.10 
82.00 
74 .67 
72.85 
82.02 
76.88 
70.68 
63  .05 


100 .37 
100.63 
99.50 
100.10 
99.67 
99.40 
99.32 
99.42 


Table   10 — Series  B — Analyses  of  briquettes  in  which  dolomite   lime 

was  used. 
(Analyzed  after  exposure  of  eight  hours  in  steam  cylinder.) 


.g 

"3 

£ 

%% 

a 

O 

^ 

a) 

- 
= 

Mixture. 

ft& 

Si 

d 
o 

"c3 

o 

w 

o 

6 

-t 
O 

-4 

O 

0) 

3 

-d 

"3 

■2^ 

O 

6C 

J? 

O 

&& 

o 

fc 

oq 

Eh 

o 

a 

< 

O 

o 

m 

w 

Eh 

1 

90  parts  coarse  sand;  10  parts  dolo- 

mite  

5 

4.98 

0.38 

3.81 

0.23 

2.21 

2.24 

0.75 

85.23 

99.45 

2 

Same  as  No.  1 

10 

4.49 

0.43 

3.45 

0.96 

2.05 

2.13 

3.14 

83 .61 

99.83 

3 

80  parts  coarse  sand;  20  parts  dolo- 

mite   

5 
10 

8.56 
9.97 

2.53 
1.92 

6.58 
7.57 

0.70 
0.95 

3.38 
3.19 

3.44 
4.39 

0.65 
1.69 

75  .80 
72.62 

99.11 

4 

Same  as  No.  3 

100.18 

5 

90  parts  fine  sand;  10  parts  dolo- 

mite   

5 
10 

4.97 
5.40 

0.92 
0.40 

3.75 
4.07 

0.68 
0.95 

2.22 
1.92 

1.82 

1.88 

1.98 
6.29 

84.23 

79.28 

99.65 

6 

Same  as  No.  5 

99.79 

7 

80  parts  fine  sand;  10  parts  dolo- 

mite  

10 

9.23 

0.79 

7.00 

0.94 

1.82 

5.74 

7.03 

67.88 

99.64 

36  STUDY    OF    SAND-LIME   BRICK. 

Table  11 — Summary  of  results  indicated  in  preceding  tables  of  analyses. 


Percentage 
of  caustic  filler 

Pressure 
of  steam  in  at- 
mospheres. 

Kind 

of  caustic  filler 

used. 

Percentage  of  soluble  silica  found 
by  analysis  of  product. 

used. 

Using  coarse 
sand. 

Using  fine 
sand. 

r 

5 

0.43 
0.75 

3.00 

10 \ 

Dolomite  lime 

1.9& 

\ 

10 

Pure  lime 

3.33 
3.14 

7.58 

Dolomite  lime 

6.29 

r 

5 

0.59 
0.65 

3.41 

1 

20.    .                                         { 

1 

10 

2.75 

11.14 

7. OS 

S.  V.  Peppel1  in  1903  studied  the  effect  of  varying  the  amount  of 
fine  and  coarse  sand  employed  in  the  mixture.     He  used  two  pure  sharp 
glass  sands  with  mechanical  analysis  as  follows : 
Coarse  sand: 
Retained  on  sieves  of.  following  meshes: 

Per 
cent. 

20    0.0 

40 50.0 

60    33.0 

80 7,0 

100     7.0 

120    2.0 

150     1.0 

Fine  sand: 

Residue  on  sieves  of  following  meshes: 

Per 
cent. 

120    1.70 

150    1.00 

200 1.25 

Average  diameter  of  grains: 

0.0212       in 24.00 

0.0086      in 19.00 

0.0004       in 8.50 

0.00026     in 7.50 

0.000136  in 5.70 

Finer    32.35 

In  each  mixture  5  per  cent  of  steam-slaked  calcium  hydrate  was  used. 
The  results,  each  being  the  average  of  three  tests,  are  shown  in  the 
following  table: 

i  Proc.  Am.  Ceramics  Soc,  vol.  5,  1903,  p.  168. 


TECHNIQUE   OF    MANUFACTURE. 


37 


Table  12 — Effect  of  coarseness  of  sand  used  in  sand-lime  brick  mixtures. 


Number.       • 

Ratio  of  coarse  to  fine  grains. 

Crushing 
strength  of  re- 
sulting 
briquette  in  lbs. 
per 
square  inch. 

Tensile 
strength  of  re- 
sulting 
briquette  in  lbs. 
per 
square  inch. 

77 

3114 

2955 
2451 

131 

79 

144 

84 

224 

Gasenapp's  tables  show  clearly  that  fineness  of  grain  is  a  factor  deter- 
mining in  part  the  completeness  of  the  reaction.  Since  this  is  so,  the 
fineness  of  the  sand  employed  in  the  mixture  is  the  index  of  the  value 
of  the  finished  product.  This  view  seems  to  have  been  accepted  and 
adopted,  in  principle  at  least,  by  the  majority  of  manufacturers.  Even 
those  who  do  not  grind,  may,  in  the  majority  of  cases,  have  at  hand  a 
natural  product  sufficiently  supplied  with  fine  material  to  answer  the 
requirements  of  this  theory.  Pepper's  tables  show,  however,  that  the 
use  of  fine  sand  is  accompanied  by  lowering  in  the  quality  of  the  bricks 
made  from  it,  at  least  in  some  respects,  as,  for  example,  in  their  crush- 
ing strengths.  Hence  it  would  seem  that  these  two  series  of  experi- 
ments lead  to  contradictory  results.  At  any  rate,  further  experimenta- 
tion is  necessary  in  order  properly  to  interpret  the  condition  involved. 
Firsthand  foremost,  it  seems  a  study  should  be  made  of  the  compounds 
formed  by  the  reaction,  that  is,  of  the  bonding  material  of  the  bricks. 
Has  it  properties  of  such  value  that  a  greater  amount  will  add  to  the 
ultimate  value  of  the  mass,  or  has  it  objectionable  features  which  would 
indicate  that  it  should  be  kept  down  to  the  minimum  point  in  the  ulti- 
mate product?  Other  considerations  also  naturally  suggest  themselves 
as  subject  for  study — for  example,  the  shape  of  the  sand  particles  used. 

From  an  examination  of  the  experiments  originally  conducted  on  the 
finely-divided  silica  of  Southern  Illinois,  referred  to  on  page  9,  it 
appeared  evident  that  a  further  study  along  the  same  line  might  show 
that  the  homogeneous  hydrosilicate,  thus  easily  produced  at  will  and 
in  any  desired  form,  would  afford  convenient  material  for  the  study  of 
its'  properties. 

An  investigation  was  therefore  undertaken  for  the  purpose  of  learning 
more  about  the  properties  of  silicates  made  from  very  fine  silica,  the 
effect  upon  them  of  the  introduction  of  varying  amounts  of  the  silica 
into  the  mixtures  used"  in  their  manufacture,  and  of  the  relative  values 
of  round  and  sharp  sand.  The  writers  prepared  bricks  from  the  mix- 
tures shown  in  the  following  tables.  The  silica  used  was  the  finely- 
divided  material  from  Southern  Illinois,  which  is  in  reality  a  very 
finely  divided  quartz.  When  properly  mounted  and  examined  under 
the  polarizing  microscope  at  a  magnification  of  about  300  diameters, 
the  silica  exhibits  very  distinctly  the  crystalline  structure  of  quartz.  A 
few  particles,  measured  by  means  of  a  micrometer  eye-piece,  show 
diameters  in  excess  of  0.02  mm.  or  .0008  in.  The  bulk  of  the  material, 
however,  is  composed  of  particles  less  than  0.01  mm.  or  .000-1  in.  in 
diameter.  For  comparison  of  their  sizes  with  the  finer  particles  used 
hy  Peppel,  see  page  36. 


38 


STUDY    OF    SAND-LIME   BRICK. 


Table  13 — Composition  of  mixtures  used  by  Parr  and  Ernest  in  the 
manufacture  of  test  bricks. 


(First   series) 

No 

Kind  of  sand  used. 

Sand. 

Lime. 

Silica. 

Weight. 

Per  cent. 

Weight. 

Per  cent. 

Weight. 

Per  cent. 

1 

23 .75 
23.75 

22.50 
22.50 

22.75 
22.75 

22.25 
22.25 

95 
95 

90 
90 

91 
91 

89 
89 

1.25 
1.25 

1.25 
1.25 

1.75 
1.75 

2.00 
2.00 

5.00 
7.50 
10.00 
12.50 

5 
5 

5 
5 

7 

7 

8 

8 

20 
30 
40 
50 

?, 

Sharp 

3 

Round 

1.25 
1.25 

0.50 
0.50 

0.75 
0.75 

20.00 
17.50 
15  .00 
12.50 

5 

4 

5 

R 

2 

fi 

Sharp 

2 

7 

Round 

3 

8 

3 

q 

80 

in 

70 

n 

60 

1? 

50 

1 

Table  14 — Composition  of  mixtures  used  by  Parr  and  Ernest  in  the 
manufacture  of  test  bricks  at  Anderson,  Indiana.  Figures  shoiv 
percentages. 

(Second  series)  • 


Number. 

Round 

sand. 

Sharp 
sand. 

Fine  sand— 
60-100. 

Fine 
silica. 

Kaolin 

(clay). 

Lime 

(CaO). 

Number 

of 

bricks 

made. 

1       

92 

8 

8 

8 

8 

8 

8 

8 

8 

8 

8 

8 

8 

8 

8 

10 

10 

10 

9 

8 

15 

10 

8 

2 

92 

9 

3 

90 

2 
2 

8 

4 

90 

8 

5 

90 

2 
2 

8 

0 

90 

8 

7 

87 

5 
5 

8 

8 

87 

8 

9 

87 

5 

5 

•  7 

10 

87 

8 

H 

85 

5 
5 

7 

7 

8 

8 

90 

66 

92 

85 

40 

2 
2 
1 
1 
2 
2 

8 

12 

85' 

8 

13 

84 

8 

14 

84 

8 

15 

80 

7 

10 

80 

• 

8 

17 

10 

18 

25 

8 

19 

9 

20 

10 

21 

25 

25 

8 

In  pressing,  a  small-sized  brick  press,  belonging  to  the  Anderson 
Foundry  &  Machine  Company,  Anderson,  Indiana,  was  used,  and  steam- 
ing was  done  in  a  small  experimental  hardening  cylinder  belonging  to 
the  same  firm.  The  bricks  were  kept  under  8  atmospheres  of  steam 
pressure  for  10  hours. 


TECHNIQUE   OF  MAHUFACTUBE. 

"All  the  bricks  made  were  tested,  with  the  results  shown  below 


39 


Table  15 — Results  of  tests  on  experimental  bricks. 
(.First  series) 


No, 


Composition. 


Sand. 


Kind. 


Per  cent. 


Lime, 
per  cent. 


Silica, 
per  cent. 


Results  of  tests 


Curshing 

strength 

in 

lbs.  per 

square 

inch. 


Trans- 
verse 
modulus 
of  rup- 
ture. 


Number 

Absorp- 

of 

tion 

bricks 

in  per 

tested. 

cent. 

Free 
lime, 
in  per 
cent'. 


Round. 
Sharp.. 
Round. 
Sharp. . 
Round. 
Sharp.. 
Round. 
Sharp.. 


790 

1]5 

420 

i;:t, 

228 

030 

1,240 

1,688 

1,732 

1.470 

1,633 

1,440 


736 

1 

8.95 

467 

4 

12.70 

228 

4 

10 .81 

297 

4 

12.31 

71 

4 

13  .60 

367 

5 

16.15 

166 

4 

14  .30 

289 

5 

18.91 

137 

5 

41 .70 

152 

4 

48.00 

416 

3 

32.95 

366 

3 

38.70 

0.10 
0.10 
0.14 

a. 22 

1.55 
0.46 
1 .36 
0.59 
0.75 
1.97 
3.14 
9.43 


Table  16 — Results  of  tests  on  experimental  bricks. 
(Second  series) 
Tests  were  made  on  six  bricks.     The  figures  given  are  the  means  of 
five  of  these. 


Composition. 

Tests. 

No. 

Round 
sand 
(20-30 

mesh)— 
Per 
cent. 

Sharp 
sand 
(20-30 
mesh)— 
Per 
cent. 

Fine 
sand 
(60-100 
mesh)— 
Per 
cent. 

Fine 
silica 
(pow- 
der)— 
Per 
cent. 

Kaolin 

(clay)— 

Per 

cent. 

Lime 

(CaO)— 

Per 

cent. 

Trans- 
verse 
modulus 

of  rup- 
ture. 

Crushing 

strength, 

in  lbs. 

per 

square 

inch. 

Absorp- 
tion, 
per 
cent  of 

dry 
brick. 

1 

92 

8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
8 
10 
10 
10 
9 
8 
15 
10 

0 
118 

0 
207 

0 
179 
155 
251 
50 
150 
147 
281 
137 
347 
181 
560 
420 
598 
614 
174 
391 

590 
1,250 

520 
1,360 

510 
1,240 
1,390 
1,920 

790 
1,640 
1,600 
2, 500 
1,870 
2,290 
2,690 
2,010 
2,450 
3,640 
3,270 
1,180 
2, 650 

14.9 

2 

92 

16.9 

3   . 

90 

2 
2 

12.7 

4 

90 

17.4 

5 

90 

2 
2 

13.4 

6 

90 

15.5 

1 .... 

87 

5 
5 

10.5 

8 



87 

13.5 

9... 

87 

5 

5 

11.7 

10  . 

87 

12.4 

11 

85 

5 
5 
7 
7 
8 
8 
90 
66 
92 
85 
40 

2 
2 

1 
1 
2» 
2 

13.9 

12 

85 

14.3 

13 

84 

11.6 

14 

84 

13  .5 

15 

80 

10.7 

16... 

80 

11.7 

17 

16.3 

18 

25 

12.8 

19 

15.1 

20 

23.2 

21 

25 

25 

13.7 

The  first  desideratum  in  the  preparation  of  the  mixture  for  the 
niiinufacture  of  sand-lime  bricks  is* to  proportion  its  various  ingredients 
in  such  a  manner,  that  as  little  difficulty  as  possible  will  be  experienced 


40  STUDY    OF    SAND-LIME   BRICK. 

in  pressing.  In  order  to  accomplish  this,  several  conditions  must  be 
kept  in  mind,  viz,  the  strength  and  trueness  of  shape  of  the  bricks 
in  the  green  condition,  and  the  effect  of  the  material  on  the  lining  of 
the  mold  boxes.  Sand  is  naturally  very  hard  on  machinery,  but  under 
some  conditions  it  cuts  much  worse  than  under  others.  In  our  expe- 
riments we  found  it  very  difficult  to  press  shapely  bricks  from  a  mix- 
ture of  round  sand  and  5  per  cent  of  lime.  With  8  per  cent  of  lime, 
however,  the  bricks  were  firm  enough  to  be  handled  easily  in  the  green 
condition.  The  ideal  mixture,  and  the  one  that  must-  be  realized  if 
bricks  are  to  be  made  successfully  on  a  commercial  basis,  is  one  in  which 
there  is  enough  fine  material  to  surround  the  larger  particles,  thus 
preventing  their  cutting  action,  and  to  allow  of  very  closely  packing. 
However,  it  is  not  desirable  to  have  all  of  the  sand  very  fine.  This 
is  shown  by  our  experience  with  mixtures  of  Illinois  silica  and  lime. 
When  such  mixtures  are  put  through  the  press  in  the  usual  way  the 
air  has  not  time  to  escape,  and  consequently  the  brick  ruptures  when 
the  pressure  is  released  from  the  mold  boxes. 

The  bricks  made  in  both  series  of  experiments  were  tested  in  the 
usual  way.  .  It  was  not  possible  to  measure  the  pressure  applied  in 
molding,  but  it  was  the  intention  of  the  operator  to  so  regulate  the 
depth  of  the  mold  box  that  each  brick  would  be  subjected  to  the  same 
amount  of  pressure. 

The  results  of  the  experiments  show  that  brick  No.  1  in  the  first 
series  of  tests  possessed  the  highest  modulus  of  transverse  fracture  and 
the  greatest  crushing  strength.  Moreover,  it  was  lowest  in  absorption. 
No.  1  in  the  second  series  was  less  satisfactory.  This  lack  of  strength 
in  the  second  brick  may  be  explained  by  the  fact  that  very  great  pressure 
had  to  be  used  in  order  to  get  a  brick  at  all  in  the  first  instance,  while 
in  the  second,  the  additional  amount  of  lime  used  made  the  brick 
stronger  in  the  green  condition;  but  it  interfered  with  the  formation 
of  the  bond.  The  absorption  is  considerably  higher  in  every  case  where 
the  sharp  sand  was  used,  but  with  the  exception  of  No.  1  of  the  second 
series,  the  brick  made  from  sharp  sand  showed  greater  strength.  The 
last  four  bricks  of  the  second  series  are  very  instructive  illustrations 
of  the  effect  of  very  fine  material.  The  absorption  in  these  was  excess- 
ively high  and  the  bricks  were  weak.  Two  per  cent  of  clay  has  appar- 
ently no  effect  on  the  strength  of  the  bricks,  while  5  per  cent  of  this 
substance  weakens  them  but  lowers  the  absorption.  Too  much  lime 
weakens  the  bond  and  increases  the  absorption,  as  shown  by  Nos.  17, 
19,  and  20. 

Our  study  of  bricks  made  from  lime  and  fine  silica  indicates  that  the 
bonding  material  is  the  weakest  part  of  the  brick,  and  that,  for  the  best 
results,  the  bond  should  be  kept  as  low  as  possible,  consistent  with  good 
bonding. 

The  statistics  on  page  34  show  that  more  than  half  of  the  plants 
operating  in  this  country  grind  a  part  of  the  sand  and  that  10  out  of 
63  grind  it  all.  In  view  of  the  fact  that  sand  grinding  is  a  very  difficult 
and  expensive  process,  it  must  be  evident  that  the  followers  of  this 
practice  expect  great  good  to  come  from  having  the  material  very  fine. 


TECHNIQUE   OF    MANUFACTURE.  41 

It  is  the  intention  of  some  operators  to  crush  the  material  until  all  of 
it  will  pass  the  100-mesh  screen.  When  grinding  is  carried  to  such  an 
extent  it  will  be  evident  that  a  large  part  of  the  sand  will  he  so  finely 
divided  that  it  will  compare  favorably  with  the  fine  Illinois  silica  which 
has  been  used  as  the  basis  for  the  preparation  of  compounds  for  this 
investigation. 

One  of  the  purposes  of  this  work  was  to  study  the  character  of  com- 
pounds made  from  extremely  fine  material,  and  in  the  bricks  numbered 
9,  10,  11,  and  12,  we  have  this  condition  realized.  A  glance  at  the 
results  presented  in  the  preceding  table  will  show  that  despite  the  fact 
that  excessively  large  amounts  of  lime  were  used  in  these  bricks,  they 
were  of  a  poor  grade.  Those  samples  in  which  smaller  quantities  of 
lime  were  employed  lacked  coherence.     (See  plate  III.) 

It  would  seem  that  where  the  material  is  very  finely  divided  the 
molecular  ratio  of  lime  to  silica  required  for  a  satisfactory  product 
should  be  nearly  one.  It  can  be  readily  seen  that  the  finer  the  sand, 
the  greater  is  the  amount  of  lime  required  to  yield  a  coherent  mass.  If 
the  sand  particles  are  to  be  welded  together  by  the  steaming  process,  it 
is  evident  that .  each  must  be  surrounded  by  a  film  of  lime.  If  we 
assume  that  this  film  is  of  uniform  thickness,  then  the  amount  of  lime 
needed  to  produce  the  bond  will  be  directly  proportional  to  the  total 
surface  of  the  particles  and  inversely  proportional  to  the  square  of  their 
mean  diameters.  This  relation,  however,  holds  only  to  a  point  beyond 
which  the  sand  grains  are  so  small  that  the  reaction  penetrates  their 
masses  and  converts  the  entire  mixture  into  a  homogeneous  calcium 
silicate?  Our  experiments  show  that  when  very  fine  silica  was  used  in 
the  mixture  the  amount  of  lime  necessary  to  give  a  strong  coherent 
mass  was  nearly  equal  to  that  of  the  silica  used. 

From  the  foregoing  discussion  it  would  seem  that  to  make  the  best 
bricks  with  the  minimum  amount  of  lime  the  aim  of  the  manufacturer 
should  be  to  keep  the  ratio  of  quartz  to  bond  in  his  brick  as  high  as; 
]Dossible.  To  effect  this,  however,  there  must  be  a  gradation  in  the  size 
of  the  sand  used  from  coarse  to  that  which  will  just  pass  a  100-mesh 
sieve.  The  use  of  very  much  material  finer  than  this  is  not  advisable, 
since  it  would  increase  the  amount  of  porous  bonding  material.  Figures 
A  and  B  of  plate  IV  are  photographs  of  magnified  sand-lime  brick 
sections,  as  seen  in  polarized  light.  The  relatively  large  amount  of 
bonding  material  in  figure  B,  as  compared  with  that  in  figure  A,  is 
noticeable. 

Xo  fixed  rule  can  be  laid  down  for  the  proper  proportioning  of  the 
various  sizes  of  sand,  since  this  is  a  matter  that  will  depend  largely  on 
the  peculiarities  of  each  particular  sand.  It  may  be  stated,  however, 
that  in  any  case  sizes  ranging  from  about  60  to  100  mesh  should  pre- 
dominate, with  only  enough  of  the  finer  particles  to  occupy  the  inter- 
stices between  the  larger  ones. 

While  it  is  true  that  in  some  respects  the  bricks  made  from  round 
sand  were  the  best,  it  must  be  remembered  that  there  are  other  considera- 
tions to  be  weighed  in  any  final  conclusion  as  to  the  best  condition  in 
which  to  have 'the  sand.     In  our  experiments  there  was  some  difficulty 


42  STUDY    OF    SAND-LIME   BRICK. 

in  pressing  the  bricks  in  which  the  round  sand  was  used,  and  in  the 
case  of  the  first  sample  this  operation  was  almost  impossible.  The 
photographs  in  plate  III  show  the  effect  of  handling  bricks  in  which 
round  and  sharp  sands  were  -used.  Those  in  which  round  sand  was 
used  are  worn  at  the  corners  and  their  sides  are  rough,  while  the  others,, 
made  with  sharp  sand,  retain  their  sharp  corners  and  have  smooth  sides. 

CONCLUSIONS. 

From  a  consideration  of  our  own  experiments  and  a  study  of  the 
literature  on  the  subject,  the  following  conclusions  with  reference  to 
the  character  of  the  sand  used  in  mixtures  for  sand-lime  brick  appear 
to  be  warranted : 

1.  Sand  or  silica  may  be  brought  to  such  a  degree  of  fineness 
that  the  reaction  with  lime  will  proceed  throughout  the  parti- 
cles, forming  a  homogeneous  hydrosilicate  with  distinctive 
properties  which  are  imparted  to  the  brick  in  direct  proportion 
to  the  amount  of  such  material  present. 

2.  Some  fine  material  is  necessary  in  order  to  give  the  mixture 
a  consistency  such  that  it  will  mold  easily  into  bricks,  which 
in  the  green  condition  will  be  strong  enough  to  be  handled. 

-  3.  The  properties  of  the  compound  resulting  from  the  inter- 
action of  lime  and  very  fine  silica  are  not  desirable  in  a 
building  brick,  and  consequently  in  sand-lime  brick  the 
amount  of  this  compound  present  in  the  brick  should  be  kept 
as  low  as  possible. 

4.  The  quantity  of  lime  needed  to  give  a  strong  coherent  mass 
will  vary  directly  as,  (a)  the  surface  factor  of  the  sand  par- 
ticles; and  (b)  the  amount  of  superfinely  divided  silica. 

5.  The  character  of  the  sand  particles  (whether  round  or  sharp) 
must  be  considered  from  the  standpoint  of  the  effect  on  both 
the  green  brick  and  the  finished  product.  The  best  condition 
would  appear  to  be  found  in  a  mixture  of  both  round  and 
sharp  sand.  * 

The  Effect  of  Impurities  in  Sand. 

The  effect  of  clay  upon  the  quality  of  sand-lime  bricks  has  been 
studied  by  S.  V.  Peppel,1  who  concludes  that  this  constituent,  when  not 
in  excess  of  10  or  12  per  cent  of  the  mixture,  is  not  injurious  to  the 
bricks.  On  the  other  hand,  it  adds  to  the  ease  with  which  the  bricks 
may  be  molded,  and  consequently,  in  small  amounts,  may  be  considered 
beneficial  rather  than  detrimental2  to  the  mixture. 

Since  kaolin  is  the  base  of  all  clays,  Peppel  in  his  experiments  used 
this  as  representing  the  hydrated  silicates.  Feldspar  was  employed  as 
representing  the  anhydrous  silicates.  The  following  tables  are  reprinted 
from  PeppeFs  paper: 


i  Proc.  Am.  Ceramic  Soc,  vol.  5,  1903,  p.  168. 

2  A  glance  at  the  table  on  page  38  will  show  that  while  the  substitution  for  2  percent  and  5  per  cent 
of  the  coarse  sand  in  the  mixture  of  an  equal  quantity  of  kaolin  proves  beneficial  to  the  bricks,  the  bene- 
ficial effect  is  not  as  great  as  if  fine  sand  had  been  used  in  its  place. 


ILLINOIS  STATE  GEOLOGICAL  SURVEY. 


Bull.  No.  18,  Plate  III. 


Photographs  of  sand-lime  bricks  containing  fine-grained  quartz,  and  different 

proportions  of  lime. 


TKl'irNIQUB   OF    MANUFACTTl.'K. 


43 


Table  1  •' — Effect  of  clay  in  sand-lime  brick  mixtures  upon  the  quality 
of  the  resulting  bricks. 

(By  S.  V.  Peppel) 

Data : 

Steam  pressure — 150  pounds  per  square  inch. 
Temperature  in  hardening  cylinder — 185°  C. 
Time  exposed  to  steam — 10  hours. 
Molding  pressure — 10,000  pounds  per  square  inch. 


Composition  of  mixtures. 


■SB 

a  .a 


Per  cent 
quicklime. 


AY  hen  tested. 


At  once  after 
hardening. 


g"S 
O 


After 

aging. 

■ 

-a 

rj  M 

_   tlC 

■a  c 

,a  a> 

•s  *> 

gin 

g-B 

O 

E-< 

After 
freezing. 


■3  G 


g13 


.CO 

|>  a 


4 
4 
4 
4 

3 
3 

4 
4 

3 
3 
3 
3 

2 
2 

2 
2 

1 

1 
1 
1 

2 

1 
1 

......... 

2 

1 

1 

1 
1 

2.5 
5.0 
10.0 
20.0 

5 

5 
5 
5 

5 
5 

5 
20 

5 
10 

10 
10 

2 

2.5 
5.0 

2 
2 

5 
5 

""io" 

10 
10 

10 

2,766 
2,500 
1,943 
1,705 

3,697 
2,260 

3,835 
3,340 

2,260 
4,729 
3,697 
5,607 

7,745 

5,872 

5.187 
4,429 


338 
210 
184 
162 

2,449 
2,376 
1,687 
1,325 

194 
277 
157 
138 

4?7 

238 

1,846 

187 

351 
295 

3,955 
3,342 

364 
175 

238 
599 
497 

1,846 
3,780 

187 
596 

503 

5, 843 

446 

437 

593 

?,86 

445 

2,917 
2,481 
1,910 
1,477 

3,812 
2,117 

4,502 

3,887 

2,117 
5,957 
3,812 
7,525 

9,007 
6, 194 

5.853 

4,818 


219 
181 
121 
93 

215 
156 

352 


156 

480 


371 
561 


314 

459 


8.32 
8.00 
8.50 
9.00 

8.06 
10.36 

8.62 


8.62 
6.41 


9.11 
8.05 


The  effect  of  feldspar  as  one  of  the  impurities  in  sand  was  also 
studied,  but  not  with  the  same  degree  of  fullness  as  was  that  of  clay. 
The  results  are  shown  in  the  following  table : 


1  A  is  the  average  of  tests  number  106,  107,  108,  109,  110  and  111. 

2  C  is  the  average  of  tests  number  118,  119  and  120. 

3  B  is  the  average  of  tests  number  112,  113,  114,  115,  116  and  117. 
<  D  is  the  average  of  tests  number  121,  122  and  123. 


44  STUDY    OF    SAND-LIME   BRICK. 

Table  18 — Effect  of  feldspar  in  sand-lime  brick  mixtures. 

(By  S.  V.  Peppel) 
Data: 

Steam  pressure — 150  pounds  per  square  inch. 
Temperature  in  hardening  cylinder — 185°  C. 
Time  exposed  to  steam — 10  hours. 
Molding  pressure — 15,000  pounds  per  square  inch. 


Composition  of  mixture. 

When  tested. 

Ej 

Per  cent 

At  once  after 

After 

After 

•a  o 

£ 

X) 

c3 

-o  B 
a  p. 

a 

a 

quicklime. 

hardening. 

aging. 

freezing. 

.9* 

-3  Hi 

OJ 

<U 

>o 

o  £ 

o 

2 

to 

d 

'  J3 

g 

fii 

a 

A 

A 

03 

B 

o 
o 

i.s. 

d 

o 

1 

a  w 

«2 

li 

■31 

■a  a 

•2  S 

8  a 

a 

08  O^ 

t-i 

0> 

3 

o 

E"S 

§M 

3  to 

4)   «1 

=    OT 

S   OT 

£ 

Ph 

Ph 

pu 

Ph 

ft 

o 

H 

o 

El 

O 

Eh 

Ri 

2 

1 

0 

10 

5,187 

286 

5,853 

314 

9.11 

F2 

2 

1 

10 

10 

4,619 

339 

5,115 

197 

6.94 

The  effect  of  replacing  sand  with  feldspar  to  the  extent  of  10  per  cent 
is  not  to  diminish  the  strength  of  the  brick.  Although  there  is  a  slight 
decrease  in  its  crushing  strength  there  is  an  increase  in  its  tensile 
strength. 

It  has  been  generally  supposed  that  lime  and  feldspar  would  not 
react  when  mixed  and  steamed  after  the  manner  of  hardening  sand- 
lime  bricks,  but  some  recent  work  in  the  chemical  laboratory  of  the 
University  of  Illinois  appears  to  give  evidence  to  the  contrary;  but 
whether  these  two  substances  react  or  not  is  of  very  little  consequence 
to  the  sand-lime  brick  industry,  as  feldspar  is  seldom  found  in  sand  in 
sufficient  quantities  to  be  detrimental. 

Eaw  clay,  when  mixed  with  lime  and  steamed,  will  not  react  with  it 
as  quartz  does.  If,  however,  the  clay  be  calcined  to  500° C.  and  pulver- 
ized and  then  mixed  with  slaked  lime,  the  two  will  unite  forming  a 
sort  of  cement.  This  fact  is  made  use  of  in  .the  manufacture  of  low- 
grade  cements  from  calcined  clay  and  lime.  If  the  calcination  of  the 
clay  be  carried  to  900°.  instead  of  500°,  the  mixtures  with  lime  will  not 
set,  but  they  may  be  hardened  by  the  action  of  steam.  This  fact  was 
brought  out  by  J.  M.  Knote3  in  a  recent  paper  before  the  American 
Ceramic  Society  in  Pittsburg.  It  would  thus  seem  that  sands  contain- 
ing large  amounts  of  clay  might  be  rendered  suitable  for  the  manufac- 
ture of  sand-lime  bricks  by  being  subjected  to  preliminary  roasting. 


Pressure  in  Molding  Bricks. 

The  object  to  be  accomplished  in  pressing  mixtures  in  brick  making 
is  not  only  to  shape  the  mass  and  give  it  sufficient  strength  to  stand  up 
in  the  hardening  cylinder,  but  also  to  bring  the  reacting  materials  into 


„..j  average  of  tests  number  112,  113,  114,  115,  116,  and  117. 

2  JT  jg  the  average  +  QC*"°  T-ii-i-mKnr.   10^1      10£  a-nrl    1  OA 


i  R  is  the 


le  average  tests  number  124,  125  and  126. 
Proc.  Am.  Ceramic  Society,  vol.  12,  1910,  p.  233. 


ILLINOIS  STATE  GEOLOGICAL  SURVEY.  Bull.  No.  18,  Plate  IV. 


Apparatus  used  for  hardening  mixtures  of  lime  and  silica  by  steam. 


TECHNIQUE    OF    M  A  N W  FA  ('TUBE. 


45 


close  enough  contact  so  that  chemical  reaction  can  take  place.  The 
ideal  condition  is  reached  when  the  sand  grains  are  pressed  closely 
together  with  only  a  film  of  lime  between  them.  The  most  economic 
pressure  to  use  in  any  case  will  vary,  it  would  seem,  with  the  character 
of  the  mixture.  Peppel  finds  that  the  best  results  are  obtained  when 
15,000  pounds  pressure  is  applied  for  each  square  inch  of  surface,  and 
that  pressures  higher  than  this  produce  bricks  of  lower  crushing  strength. 
This  is  a  question  of  very  great  importance,  for,  while  it  seems  improb- 
able that  pressure  too  great  for  the  good  of  the  brick  is  likely  to  be 
employed,  nevertheless  there  is  a  limit  beyond  which  it  is  poor  economy 
to  carry  it,  because  of  possible  evil  effects  on  the  mold  liners. 

The  character  of  the  sand  grains  has  much  to  do  with  the  matter  of 
pressjng,  for,  while  the  same  pressure  was  used  in  molding  all  the 
mixtures  studied  by  the  authors,  those  mixtures  containing  round  sand 
grains  produced  bricks  with  the  lower  absorption.  This  can  be  accounted 
for  only  by  supposing  that  the  round  grains  move  on  one  another  more 
rapidly,  pack  more  closely  and  leave  less  room  between  them  than  do 
sharp  grains. 

If  the  material  to  be  pressed  is  very  fine,  presses' must  be  constructed 
so  as  to  allow  air  to  escape.  This  is  accomplished  in  some  presses  by 
causing  the  die  first  to  descend,  then  to  rise  a  little,  and  finally  to 
descend  again  for  the  final  compression.  By  this  procedure  any  air 
which  is  unable  to  escape  during  the  first  plunge  of  the  die  and  which 
might  rupture  the  brick  if  allowed  to  remain,  escapes  when  the  die  is 
raised. 

Hardening  Bricks. 

It  is  very  essential  that  the  cylinder  used  in  hardening  the  bricks 
be  well  constructed,  for  weaknesses  in  this  part  of  the  equipment  are 
dangerous.  The  usual  practice  is  to  steam  for  10  hours  at  120  pounds 
pressure  per  square  inch.  Some  experiments  were  undertaken  by  Pep- 
pel for  the  purpose  of  determining  the  best  condition  uncler  which 
hardening  should  be  accomplished.     His  results  are  quoted  below : 


Table  19 — Effect  of  time  and  pressure  in  hardening  process  upon  the 
quality  of  sandr-lime  brick. 

(By  S:  V.  Peppel) 
Steam  pressure,  150  pounds. 


Hours  in  steam. 

A. 

B. 

C. 

D. 

E. 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.  > 

T.  S.2 

4 

7,896 
7,994 
7,404 
7,767 
7,514 
7,894 

544 
390 
509 
464 
337 
380 

5,303 
5,045 
4,957 
4,902 
5,064 
5,849 

392 
199 
262 
284 
250 
329 

5,282 

591 

4,514 

470 

4,441 

330 

6... 

8 

6,170 

632 

4,249 

430 

4,491 

337 

10 

12 

14... 

6,165 

556 

4,543 

434 

4,924 

349 

4G 


STUDY    OF    SAND-LIME   BRICK. 

Steam  pressure,  120  pounds. 


Hours  in  steam. 

A. 

B. 

C. 

D. 

E. 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.i 

T.  b.2 

C.  S.i 

T.  S.2 

4 

6,989 
7,063 
8,545 

5,989 
6,495 
6,038 

5,403 

4,300 

5,760 

6 

8 

5,868 

5,142 

6,718 

Steam  pressure,  100  pounds. 


Hours  in  steam. 

A. 

B. 

C. 

D. 

E. 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C.  S.i 

T.  S.2 

C,  S.  i 

T.  S.2 

4 

6,385 
7,566 
7,494 

:::•::::: 

5,921 
X),  507 
5,753 

4,280 
5,564 

4,048 
4,456 

4,588 
6,544 

8 

12 

The  conclusion  deduced  from  this  work  is  that  four  hours  at  150 
pounds  steam  pressure  is  sufficient  to  make  good  bricks;  that  from  six 
to  eight  hours  are  required  at  120  pounds;  and  from  eight  to  12  hours 
at  100  pounds. 


1  C.  S.  is  crushing  strength,  lbs.  per  square  inch. 

2  T.  S.  is  tensile  strength,  lbs.  per  square  inch. 


4: 


THE  CHEMISTRY  OF  SAND-LIME  BRICKS. 


Review  of  Previous  Work. 

The  literature  of  sand-lime  bricks  is  not  very  extensive,  and  that 
which  has  appeared,  with  few  exceptions,  has  dealt  only  with  the  tech- 
nology of  the  subject.  It  has  been  known  from  the  very  beginning  of 
the  industry  that  the  bond  in  sand-lime  bricks  is  a  hydrated  calcium 
silicate.  This  was  an  easy  matter  to  determine,  for  it  was  known  that 
if  pure  lime  and  pure  silica  produce  a  bond  a  calcium  silicate  must  be 
formed.  Furthermore,  it  was  easy  to  determine  that  when  lime  is 
steamed  with  quartz  it  renders  some  of  the  silica  soluble,  and  that  in 
the  product  a  certain  amount  of  water  is  held  in  chemical  combination. 
Further  than  this  no  satisfactory  evidence  as  to  the  composition  and 
properties  of  the  bond  of  sand-lime  bricks  has  appeared.  Its  nature, 
therefore,  is  largely  an  unsolved  problem. 

The  hypothesis  has  been  advanced  that  the  bond  of  a  sand-lime  brick 
resembles  very  closely  some  of  the  calcium  silicates  in  set  Portland 
cement.  This  assumption  appears  to  be  quite  plausible,  inasmuch  as 
the  calcium  silicates  found  in  set  Portland  cement  are  formed  by  the 
combination  of  the  calcium  hydroxide  and  silicic  acid  resulting  from 
the  hydrolysis  of  the  ground  clinker.  But  whether  this  is  true  or  not, 
it  is  merely  conjecture,  and  there  is  no  direct  evidence  either  for  or 
against  the  assumption. 

An  article  by  George  F.  Ransom,1  devoted  to  a  discussion  of  the 
chemistry  of  sand-lime  bricks  appeared  several  years  ago.  In  this  the 
writer  shows  that  a  change  takes  place  in  the  nature  of  a  sand-lime 
brick  during  the  hardening  processes,  and  that  this  change  can  not  be 
physical,  and,  consequently,  must  be  chemical  in  its  nature.  In  the 
latter  part  of  his  article,  the  author  develops  the  fact  that  a  hydrated 
calcium  silicate  must  be  formed.     His  conclusion  is  quoted: 

"Therefore,  I  claim  that  a  chemical  change  does  take  place  during 
the  steaming,  and  that  the  bonding  material  is  calcium  hydrosilicate." 

This  article  is  only  a  verification  of  the  claims  made  in  the  original 
Michaelis  patent,  and  in  reality  adds  nothing  to  our  knowledge  of  the 
chemistry  of  the  bonding  material. 

In  a  recent  issue  of  the  Mineral  Resources  of  the  United  States  Edwin 
C.  Eckel2  states  that  chemical  methods  are  of  no  value  in  determining 


i  Rock  Products,  vol.  7,  1907,  p.  49. 

2  Mineral  Resources  of  the  United  States,  1906,  U.  S.  Geol.  Survey,  Washington,  1907,  p.  991. 


48  STUDY    OF   SAND-LIME   BRICK. 

the  nature  of  the  bond  in  sand-lime  bricks,  and  that  only  those  processes 
involving  the  use  of  the  petrographic  microscope  give  any  promise  of- 
success  in  the  solution  of  the  problem.  He  accordingly  submitted 
specimens  of  sand-lime  bricks  for  examination  to  Frederick  E.  Wright 
of  the  Geophysical  Laboratory  of  the  Carnepie  Institution,  with  the 
following  results : 

"Mr."  Wright  states  that  the  binding  material  of  these  specimens  is  a 
hydrous  lime  silicate  somewhat  akin  to  the  familiar  minerals  of  the 
zeolite  group.  The  reactions  involved  in  the  formation  of  such  hydrous 
silicate,  from  lime  and  sand  in  the  presence  of  steam,  are  simple  and 
well  known.  It  is  to  be  noted,  however,  that  these  reactions  are  in  no 
way  comparable  to  those  which  take  place  during  Portland-cement  manu- 
facture and  that  the  binding  material  of  sand-lime  brick  is  very  different 
in  composition  and  relationship  from  Portland-cement  clinker. 

It  may  safely  be  assumed,  then,  that  a  sand-lime  brick  as  marketed 
consists  of  (1)  sand  grains  held  together  by  a  network  of  (2)  hydrous 
lime  silicate,  with  probably  (if  a  magnesian  lime  were  used)  some 
allied  magnesium  silicate,  and  (3)  lime  hydrate  or  a  mixture  of  lime 
and  magnesia  hydrates.  These  three  elements  will  always  be  present, 
and  the  structural  value  of  the  brick  will  depend  in  large  part  on  the 
relative  percentages  in  which  the  sand,  the  silicates,  and  the  hydrates 
occur." 

Mr.  Eckel  appears  to  be  convinced  that  the  bonding  material  of  sand- 
lime  brick  is  a  very  different  thing  from  the  calcium  silicates  found  in 
Portland-cement  clinker.  But  Portland-cement  clinker  is  also  a  very 
different  thing  from  the  set  cement,  and  certainly  no  one  familiar  with 
the  processes  of  manufacture  of  both  sand-lime  brick  and  Portland- 
cement  would  attempt  to  defend  the  proposition  that  these  two  sub- 
stances have  very  much  in  common.  There  is  good  reason,  however, 
for  supposing  that  some  of  the  silicates  in  the  set  cement  are  identical 
with  those  to  be  found  in  the  bonding  material  of  sand-lime  brick,  and 
petrographic  or  any  other  evidence  on  the  subject  would  be  quite  wel- 
come indeed.  A  brief  discussion  as  to  the  availability  of  the  petrographic 
microscope  for  research  on  this  subject  will  be  taken  up  later. 

Notwithstanding  the  conclusion  of  Mr.  Eckel,  it  was  still  thought 
that  chemical  methods  might  give  some  valuable  information  on  this 
very  interesting  subject.  Work  was  accordingly  begun  on  this  problem 
in  the  fall  of  the  year  1907,  and  pursued  to  some  extent  throughout  the 
year.  The  fine-grained  silica  from  Southern  Illinois  was  used  in  part 
as  the  silicious  component  of  the  mixture,  and  the  results  of  the  investi- 
gation were  embodied  in  a  thesis  submitted  to  the  chemical  faculty  of 
the  University  of  Illinois  as  a  part  of  the  requirements  for  the  degree 
of  master  of  arts  in  June  of  the  following  year. 

In  working  with  the  finely  divided  silica  it  was  found  that  by  mixing- 
it  intimately  with  lime  in  equal  proportions,  pressing,  and  steaming,  a 
reaction  was  brought  about  that  resulted  in  the  formation  of  a  nearly 
homogeneous  calcium  silicate.  This  was  supposed  to  be  very  nearly  the 
same  as  the  bonding  material  of  sand-lime  bricks,  and  a  study  of  it  was 
therefore  undertaken.     By  determining  the  free  and  combined  lime  and 


CHEMISTRY    OF    SAND-LIME    BRICKS.  49 

the  combined  silica  in  the  product  it  was  possible  to  find  approximately 
the  proportions  in  which  these  materials  react.  As  a  result  of  a  number 
of  analyses,  it  was  learned  that  the  reaction  was  most  complete  when 
the  lime  and  silica  were  employed  in  equal  quantities.  Bricks  made 
from  lime  and  siliea  also  showed  greatest  strength  when  the  percentages 
of  lime  and- siliea  used  in  the  mixture  were  about  equal.  This  led  to 
the  conclusion  that  the  formula  for  the  calcium  silicate  in  the  bond  of 
the  bricks  is  CaSi03x(H20).  Determinations  of  the  combined  water. 
se<  med  to  indicate  also  that  one  molecule  of  water  was  combined  with 
one  of  lime  and  one  of  silica,  and  the  opinion  was  advanced  thai: 
CaO.SiOo.HoO  was  the  most  probable  formula  of  the  compound. 

Chemical  Investigation. 

theoretical. 

When  mixtures  of  lime  and  silica  are  subjected  to  the  action  of  satu- 
rated steam  at  various  temperatures  combination  takes  place  with  the 
formation  of  one  or  more  hydrous  calcium  silicates.  The  proportions 
in  which  these  constituents  combine  are  not  known,  so  that  to  express 
the  reaction  requires  an  equation  something  like  the  following: 
(*o+Xi+x2    ..-)    CaO+(y0+y1+y2    :..  )Si02+(z0+z1+z2)H20  = 

x0  CaO.y0  SiO2z0  H^+x,  CaO,VlSi02.z,H20. 
It  might  be  supposed  that  the  compounds  formed  are  comparatively 
simple  and  that  the  lime-silica  ratio  in  the  products  of  the  reaction 
might  in  some  way  be  influenced  by  the  proportions  in  which  the  lime 
and  silica  are  present  in  the  uncombined  condition,  as  is  the  case  with 
silicates  formed  by  fusion.  And,  furthermore,  with  a  given  lime-silica 
ratio,  we  would  expect  that  only  one  compound  would  exist  in  equilib- 
rium with  water  vapor  at  a  series  of  temperatures  and  pressures  corre- 
sponding to  those  of  saturated  steam,  i.  e.,  the  one  possessing  the  highest 
vapor  pressure.  For  if  a  calcium  silicate  having  a  lower  vapor  pressure 
were  present  under  these  conditions,  •  it  would  take  up  water  and  pass 
into  the  phase  with  higher  vapor  pressure.  Furthermore,  the  vapor 
pressure  of  any  such  silicates  formed  must  be  lower  than  the  pressure 
of  saturated  steam  at  any  definite  temperature,  for  if  it  were  higher  it 
would*  lose  water  and  revert  to  a  phase  with  lower  vapor  pressure. 
Furthermore,  the  vapor  pressure  of  any  such  silicates  formed  must  be 
lower  than  the  pressure  of  saturated  steam  at  any  definite  temperature, 
for  if  it  were  higher  it  would  lose  water  and  revert  to  a  phase  with  lower 
vapor  pressure. 

By  the  help  of  the  phase  rule  we  are  enabled  to  show  this  to  be  true. 
If  we  assume  the  simplest  case — that  from  lime  and  siliea,  calcium 
silicate  is  formed  reversibly,  thus:  CaO+Si()2+H2O^CaO.Si02.H20 
— we  will  have  as  components,  CaO,  Si02J  and  HJ),  while  the  phases 
will  be  water  vapor,  Ca(OH)2,  Si02,  and  the  compound  CaO.Si02.H20. 
The  following  relation  must  hold  true: 

P+F=C+2. 

—4  G 


50  STUDY   OF   SAND-LIME    BRICK. 

in  which  P=phases,  1  —degrees  of  freedom,  and  C— components.  Sub- 
stituting in  this  formula  and  solving  for  F  we  have  F=l.  This  means 
that  there  is  but  one  independent  variable  (temperature  or  pressure), 
or,  that  a  definite  temperature  necessitates  a  corresponding  definite 
pressure  of  water  vapor  from  the  compound.  A  system  in  which  two 
compounds  of  the  form  CaO.Si02.H20  would  be  in  equilibrium  with 
aqueous  vapor  would  be  an  invariant  one,  obtainable  at  a  single  tem- 
perature and  pressure  only.  Since  the  products  of  the  union  of  lime 
and  silica  under  the  conditions  of  manufacture  of  sand-lime  bricks 
are  stable  over  quite  a  range  of  temperature  under  the  pressure  of  satu- 
rated steam,  it  is  evident  that  there  can  be  present  but  one  hydrate  for 
each  lime-silica  ratio  used. 

We  can  also  examine  this  reaction  as  a  whole  in  the  light  of  the 
phase  rule  and  see  what  would  be  possible  if  the  reaction  proceeded 
under  equilibrium  conditions  as  represented  in  the  general  equation 
shown  above.  The  number  of  components  is  the  same  as  before ;  namely, 
CaO,  Si02,  and  H20.  The  reaction  is  one  coming  under  the  reversible 
class,  hence  there  will  always  be  present  some  Ca(OH)2  and  Si02, 
together  with  water  vapor  and  the  solid  compound.  Now,  as  before, 
two  solid  phases  cannot  he  present  in  equilibrium  except  at  a  single 
temperature  and  pressure.  It  is  possible,  however,  that  a  compound 
may  be  formed  under  one  set  of  conditions,  and  because  of  the  slowness 
with  which  the  reaction  proceeds,  still  exist  under  other  conditions, 
even  when  it  is  not  the.  stable  form  under  these  conditions. 

If  a  system  composed  of  lime,  silica,  and  water  vapor  be  in  equilib- 
rium at,  say,  100°  and  under  one  atmosphere  pressure,  then  a  change 
in  temperature  which  would  result  in  raising  the  pressure  to  ten  atmos- 
pheres, if  it  produced  a  change  in  the  equilibrium  at  all,  would  cause 
it  to  shift  in  the  direction  corresponding  to  an  absorption  of  water 
vapor  or  an  absorption  of  heat.  Both  these  changes  may  occur  simul- 
taneously, however,  or  they  may  occur  in  opposite  directions,  in  which 
case  the  one  having  greatest  effect  will  be  in  the  direction  tending  to 
maintain  the  original  conditions.  This  means  that  a  compound,  stable 
under  the  conditions  of  lower  temperature  and  pressure,  might  decom- 
pose, giving  off  some  or  all  of  its  water  at  the  higher  pressure,  but  in 
this  case  the  heat  absorbed  would  exert  a  greater  influence  toward  the 
maintenance  of  the  original  conditions  than  the  dissociated  water  vapor 
would  exert  toward  destroying  them. 

In  any  attempt  to  determine  the  chemical  composition  or  formula 
of  a  substance,  the  first  consideration  is  to  get  it  pure,  or  to  work  out  a 
method  whereby  analysis  can  be  carried  out  in  the  presence  of  impuri- 
ties. In  the  production  of  sand-lime  bricks  the  reaction  is  never  com- 
plete; consequently,  there  is  always  a  mixture  of  the  original  materials 
together  with  the  compound  or  compounds  formed. 

In  the  pursuit  of  this  work  two  general  methods  were  followed  in  the 
preparation  of  the  material  for  analyses.  In  one  of  these  a  small  per- 
centage of  lime  was  used,  and  in  the  other  a  small  percentage  of  silica. 
The  mass  action  law  teaches  that  in  a  reversible  reaction  the  ratio  of 
the  products  of  the  concentration    (raised  to  powers  corresponding  to 


CHEMISTRY    OF    SAND-LIME   BRICKS.  51 

thr  number  of  parts  entering  into  the  reaction)  of  the  constituents  on 
each  side  of  the  equation  is  a  constant,  and  this  holds  at  least  qualita- 
tively for  all  chemical  reactions.  Thus,  by  increasing  the  amount  of 
lime  used  in  a  mixture  and  using  only  a  small  amount  of  very  finely 
divided  silica,  it  is  safe  to  assume  that  practically  all  the  silica  will 
enter,  into  combination.  If  this  be  true,  the  first  step-in  the  solution 
of  the  problem  is  to  remove  the  uncombined  lime  without  decomposing 
the  calcium  silicate.  Another  method  of  attack  consists  in  using  only 
a  small  amount  of  lime  with  quartz  of  such  size  that  it  will  be  readily 
attacked  by  the  lime,  but  not  so  small  that  it  will  be  appreciably  soluble 
in  dilute  alkalies.     Both  these  methods  were  used  in  these  experiments. 

PREPARATION    OF    MATERIALS    FOR    ANALYSIS. 

'Flic  lime  used  in  the  preparation  of  the  compounds  to  be  analyzed 
Mas  Kahlbaum's  best  calcium  oxide,  burned  from  pure  marble.  It  was 
slaked  in  a  beaker  placed  in  a  desiccator  over  sticks  of  caustic  potash. 
The  slaking  was  done  by  placing  another  beaker  containing  water  in 
the  desiccator  with  the  lime  and  exhausting  the  air.  As  the  water 
evaporated,  it  combined  with  the  lime  which  crumbled  to  a  powder  and 
was  afterward  sifted  out  from  any  remaining  lumps  and  kept  in  a 
desiccator  over  caustic  potash. 

The  finely  divided  silica  was  prepared  by  precipitating  silicic  acid 
from  sodium  silicate  by  the  use  of  hydrochloric  acid,  evaporating  to 
dryness  and  washing  out  the  sodium  chloride.  By  this  process  a  very 
fine,  pure  product  was  obtained  which  was  kept  in  a  bottle  for  use. 

Two  grades  of  sand  were  prepared  by  grinding  crushed  quartz  and 
standard  Ottawa  sand.  The  material  was  run  through  a  disk  pulverizer. 
The  coarse  and  the  very  fine  material  were  removed  and  that  which 
passed  an  80-mesh  sieve  and  was  retained  on  a  120  was  kept.  The  two 
portions  saved  were  washed  first  in  hydrochloric  acid,  then  in  chromic 
•acid,  then  in  a  solution  of  caustic  soda,  and  finallv  in  dilute  hydrochloric 
acid  and  water.  When  dry  the  two  sands  were  again  carefully  screened 
and  placed  in  suitable  containers. 

For  this  phase  of  the  work,  samples  were  not  made  by  pressure,  but 
were  merely  mixed  up  in  the  proper  proportions  and  steamed  in  suitable 
vessels.  The  apparatus  used  for  hardening  was  the  small  autoclave 
shown  in  plate  IV,  fitted  with  a  gauge  reading  kilograms  per  square 
centimeter.  It  was  capable  of  withstanding  a  pressure  of  about  25 
atmospheres  per  square  inch. 

Samples  for  analysis  were  prepared  by  weighing  out  the  proper 
amounts  of  lime  and  sand  or  silica,  mixing  in  the  dry  condition,  and 
then  adding  water  which  had  previously  been  boiled  to  expel  carbon 
dioxide,  and  again  mixing.  When  properly  blended,  the  crucibles  or 
dishes  were  placed  in  the  autoclave,  in  which  the  water  was  already 
boiling,  so  that  all  carbon  dioxide  .was  excluded,  the  lid  was  fastened 
down  and  the  -team  pressure  was  brought  up  as  quickly  as  possible, 
When  large  amounts  of  material  were  to  be  prepared  a  silver  dish  hold- 
ing about  200  cc.  was  used,  hut  in  some  cases  the  mixtures  were  "made 


52 


STUDY    OF    SAND-LIME    BRICK. 


in  platinum  crucibles.  Samples  prepared  from  fine  sand  and  low  per- 
centages of  lime,  when  treated  with  phenolphthalein,  reacted  slowly, 
thus  showing  that  the  free  lime  had  practically  all  combined  with  the 
silica.  In  samples  in  which  an  excess  of  lime  was  used  with  precipitated 
silica  there  was  always  free  lime  in  the  product.  After  making  several 
inefficient  attempts  to  remove  the  lime  by  washing  with  water,  an 
attempt  was  made  to  remove  it  with  the  aid  of  dilute  acetic  acid.  After 
preparing  the  compound  it  was  placed  in  a  beaker  with  boiled  water. 
A  few  drops  of  phenolphthalein  were  introduced  and  dilute  acetic  acid 
added  until  the  color  of  the  liquid  just  disappeared.  Upon  the  recur- 
rence of  the  color  more  acid  was  added,  and  this  procedure  was  repeated 
until  the  color  reappeared  very  slowly.  It  was  found  that  even  dilute 
acetic  acid  had  the  power  to  decompose  hydrated  lime  silicates.  How- 
ever, by  working  very  carefully,  it  was  possible  to  remove  small  amounts 
of  lime  without  appreciable  decomposition  of  the  silicates.  This  method 
was  then  combined  with  another  in  which  the  preparation  was  placed 
in  a  large  beaker  and  thoroughly  agitated  by  a  whirling  motion.  The 
lime  hydrate  being  nocculent  remained  in  suspension  longer  than  the 
silicate  and  could  be  siphoned  off.  The  final  washing  was  with  dilute 
acid,  as  before. 

Since  acetic  was  too  strong  an  acid  to  be  used  conveniently  in  this 
separation,  a  weaker  one  was  sought.  The  ionization  constants  of  some 
of  the  wreaker  acids  are  as  follows : 

Table  20 — Ionization  constants1  at  1S°. 


Boric 

H2BOT  +  H+ 

S--+H+ 

1.7X10"- 9.. 

1.2X10-  15... 

Hydrosulphic 

HS-+     H+ 

COv+H+ 

HC0T+H+ 

C2H3O—  +  H+  .... 
CSH50— +H 

9.1X10- 8 

Hydrocarbonate 

6.0X10"-11 

Carbonic 

3.0X10- 7 

Acetic 

1.8X10-  5 

Phenol 2 

1.3X10- 10 

i 

It  is  essential  that  the  substance  used  for  removing  free  lime  from 
mixtures  of  lime  and  calcium  silicate  be  not  only  inactive  on  the  silicate, 
but  that  it  form  a  soluble  compound  with  lime.  Both  phenol  and 
hydrogen  sulphide  are  very  weak  acids  and  form  soluble  compounds  with 
lime.  They  were. both  tried  and  appeared  to  be  without  action  on  the 
silicates.  The  silicate  stood  indefinitely  without  anv  apparent  decompo- 
sition, under  a  pressure  of  H2S  as  furnished  by  a  Kipp  gas  generator, 
and  all  the  lime  was  completely  washed  from  the  mixture  without  diffi- 
culty. This  acid  was  therefore  chosen  as  the  means  of. removing  the 
lime  from  the  samples  before  analysis. 

The  action  of  carbonic  acid  on  the  mixture  of  lime  and  calcium  silicate 
was  also  studied,  and  the  conclusion  was  reached .  that  the  silicate  is 


Jour.  Am.  Chem.  Soc,  vol.  31,  1909,  p.  760. 
Zeitschrift  physik.  Chem.,  vol.  32,  1900,  p.  137. 


CHEMISTRY    OF    SAND-LIME   BRICKS.  53 

completely  decomposed  by  the  action  of  this  gas,  with  the  formation  of 
calcium  carbonate  and  free  silicic  acid.  Carbonic  acid  lias  also  the  power 
to  throw  down  calcium  carbonate  from  solutions  of  calcium  sulphide 
with  the  formation  of  the  corresponding  aeid  ;  consequently,  it  was  neces- 
sary to  exclude  it  when  purifying  the  silicate. 

METHODS    OF    ANALYSIS. 

Samples  made  up  with  an  excess  of  lime  were  first  freed  of  lime,  after 
which  analysis  was  carried  out  in  the  usual  way.  The  silica  was  deter- 
mined by  treating  with  hydrochloric  acid  and  evaporating  to  dryness 
several  times.  In  the  filtrate  from  the  silica  the  lime  was  determined 
by  precipitating  as  the  oxalate,  washing  and  titrating  with  potassium 
permanganate.  The  permanganate  solution  was  standardized  against 
a  calcium  solution  of  known  strength  in  the  same  way  that  it  was  used 
in  the  determinations,  so  that  any  small  errors  inherent  in  the  method 
"would  cancel.  * 

In  samples  made  up  with  excess  of  fine  sand,  the  soluble  silica  had 
to  be  separated  from  the  unattacked  quartz.  The  work  of  Lunge  and 
Millberg1  shows  conclusively  that  in  order  to  make  this  separation  quan- 
titative the  quartz  grains  must  be  of  a  size  such  that  they  will  settle 
out  of  water  quickly.  With  "dust  fine"  quartz  powder  a  two-hour 
digestion  on  the  water  bath  with  a  1  per  cent  solution  of  sodium  car- 
bonate dissolved  2.10  per  cent  of  the  weight  of  quartz  taken.  With  a 
15  per  cent  solution  of  either  sodium  or  potassium  carbonate,  on  the 
other  hand,  only  a  very  slight  trace  of  quartz  wras  dissolved  by  a  two- 
hours'  digestion  when  the  grains  were  large  enough  to  settle  out  of 
water  readily.  Hydrated  silicates  such  as  trass,  opal,  pozzuolan,  etc. 
dissolved  almost  completely  with  the  same  treatment.' 

It  might  be  supposed  that  silicates  of  the  sort  here  studied  would 
dissolve  completely  in  acid,  but  the  separation  of  combined  silica  is  not 
so  easily  effected.  On.  the  addition  of  a  strong  acid  the  silicate  is  decom- 
posed, the  calcium  going  into  solution  as  a  salt  of  the  corresponding 
acid,  with  part  of  the  silicic  acid  precipitating  as  a  colloid  and  the 
balance  remaining  in  solution.  The  quantity  which  will  stay  in  solution 
will  depend  very  largely  on  the  concentration  of  the  acid  used.  A  strong- 
acid  will  precipitate  much  of  the  silica  while  a  very  dilute  acid  will 
precipitate  but  a  very  small  part  of  it.  Hence  the  necessity  of  following 
any  acid  treatment  with  an  alkaline  solvent  under  such  conditions  that 
the  separated  silica  may  be  redissolved  while  the  quartz  particles  are 
unattacked. 

Our  determinations  were  made  by  first  crushing  the  sample  to  be 
analyzed  in  a  manner  not  to  further  reduce  the  size  of  the  sand  particles. 
It  was  then  treated  in  a  casserole  with  250  cc.  of  a  solution  of  hydro- 
chloric acid,  made  by  diluting  the  strong  acid  (1.10  sp.  gr.)  to  ten 
times  its  volume  with  distilled  water,  and  digested  on  the  water  bath 
or  over  a  low  flame  (so  that  it  would  not  boil)  for  several  hours,  the 
time  depending  somewhat  on  the  character  of  the  sample.     It  is  quite 


Zeil.  angew.  Chem.,  1897,  pp.  393  and  425. 


54  STUDY    OF   SAND-LIME    BRICK. 

essential  that  the  acid  be  not  too  strong,  and  that  the  solution  be  kept 
from  boiling  during  the  digestion,  in  order  that  the  silicic  acid  may 
remain  in  solution  and  not  interfere  with  the  subsequent  filtration. 

After  the  digestion  was  complete,  the  solution  was  filtered  off  by 
suction  through  a  reinforced  filter.  When  the  digestion  had  been  prop- 
erly carried  out  the  filtration  was  easily  done,  but  when  the  silicic  acid 
separated  it  was  a  very  difficult  process.  After  filtration,  the  sand  was 
treated  with  a  few  cubic  centimeters  of  water  and  washed  by  decantation. 
The  filter  was  then  placed  in  the  casserole  and  100  cc.  of  water  added. 
Five  grams  of  sodium  carbonate  were  then  weighed  out  roughly  and 
added  to  the  water  in  the  casserole  and  digestion  carried  out  as  before 
for  about  an  hour,  after  which  the  solution  was  again  filtered  off.  If 
very  accurate  work  is  to  be  done  this  digestion  with  a  5  per  cent  solution 
of  sodium  carbonate  should  be  repeated.  Little  difficulty  from  clogging 
of  the  filter  is  experienced  with  these  later  filtrations. 

After  the  separation  is  complete  the  filter  papers  may  be  burned  and 
weighed.  The  soluble  silica  is  determined  in  the  filtrate  by  evaporating 
the  combined  solutions  to  dryness  on  the  water  bath  in  the  ordinary 
way,  two  evaporations  being  usually  sufficient  for  this  work.  The  lime 
is  determined  in  the  filtrate  as  before. 

When  free  lime  is  found  in  the  sample  it  is  necessary  to  remove  this, 
or  to  determine  the  amount  present,  before  proceeding  with  the  silica 
determination.  It" can  be  removed  by  treating  with  hydrogen  sulphide, 
which  converts  the  free  calcium  hydrate  to  the  sulphide  or  acid  sulphide, 
in  which  form  it  is  soluble  and  can  be  washed  out.  Care  should  be 
taken  to  use  water  from  which  the  carbon  dioxide  has  been  removed 
by  boiling,  for,  otherwise,  calcium  carbonate  will  be  precipitated  and 
will  cause  error.  In  case  the  free  lime  is  to  be  determined,  this  can 
be  done  by  allowing  the  material  to  stand  in  a  closed  flask  with  distilled 
water,  which  with  occasional  shaking  will  dissolve  the  lime,  when  an 
aliquot  part  can  be  drawn  off  and  the  lime  titrated  with  standard  acid. 
If  there  is  very  much  free  lime  the  sample  taken  should  be  small,  or 
some  sugar  should  be  added  to  the  water,  to  make  sure  that  all  the  lime 
present  dissolves.  Other  methods  might  be  used  in  special  cases,  but 
these  appear  to  be  very  satisfactory  for  all  ordinary  determinations. 

Eesults  of  Chemical  Analyses. 

silicate  no.  1. 

This  sample  was  made  with  three  parts  of  lime  to  one  of  precipitated 
silica.  Steaming  was  at  12-15  atmospheres  per  square  inch  for  10 
hours,  and  excess  lime  was  removed,  first',  by  decantation  of  the  fioccu- 
lent  hydrate,  and,  then,  by  treatment  with  phenolphthalein  and  dilute 
acetic  acid. 

The  lime-silica  ratio  as  determined  was  .674/1,  which  is  rather  high 
for  silica  owing  to  the  fact  that  some  of  the  silicate  was  decomposed 
by 'the  action  of  the  acetic  acid. 


CHEMISTRY    OF    SAND-LIME  BRICKS.  55 

SILICATE    NO.    2. 

This  sample  was  mack'  by  mixing  throe  parts  of  the  sand  prepared 
from  crushed  quartz  with  one  part  of  lime  hydrate.     The  steaming  was 
at    L2-15   atmospheres  per  square  inch  for  8  hours.     Excess  lime  was 
removed  by  treatment  with  dilute  acetic  acid. 
Lime-silica  ratio=.899/l. 

SILICATE   NO.    3. 

This  sample  was  made  in  substantially  the  same  way  as  Sample  No.  2. 
Lime-silica  ratio=.870/l. 

silicate  no.  4. 

This  sample  was  made  with  10  per  cent  of  CaO  and  the  same  crushed 
quartz.  It  was  steamed  8  hours  at  12-15  atmospheres.  The  lime  was 
washed  out  with  acetic  acid. 

Lime-silica  ratio  =.863/1. 

Water-silica  ratio=.632/l. 

Calculated  chemical  formula=9CaO.Si02.6H20. 

silicate  no.  5. 

•  This  sample  was  made  with  15  per  cent  CaO  and  fine  quartz  sand. 
Steaming  was  for  8  hours  at  15  atmospheres.  The  excess  of  lime  was- 
removed  by  boiling  with  additions  of  a  solution  of  ferric  chloride.  This 
caused  the  precipitation  of  ferric  hydroxide,  which,  being  flocculent, 
could  be  siphoned  off  with  the  supernatant  liquid.  This  process  was 
carried  on  until  the  clear  liquid  showed  no  color  with  phenolphthalein. 
The  analysis  was  carried  out  as  usual,  except  that  the  iron  had  to  be 
removed  before  determining  calcium. 

Lime-silica  ratio  =.890/1. 

Water-silica  ratio=. 508/1. 

Calculated  chemical  formula=9CaO.Si02.5H20. 

silicate  no.  6. 

This  sample  was  made  with  three  parts  of  CaO  to  one  of  precipitated 
silica.  The  ingredients  were  mixed  with  water  to  the  consistency  of  a 
thick  cream  or  slurry  and  steamed  for  8  hours  at  12-15  atmospheres. 
The  excess  lime  was  removed  by  agitating  and  decanting  flocculent  lime 
hydrate,  and,  finally,  by  additon  of  acetic  acid  and  phenolphthalein  and 
washing. 

Lime-silica  ratio=.847/l. 

silicate  no.  7. 

This  sample  was  made  with  10  per  cent  CaO  and  the  fine  crushed 
quartz  sand  used  before,  steamed  for  8  hours  at  15  atmospheres.  The 
lime  was  practically  all  combined. 

Lime-silica  ratio=.818/l. 


56  STUDY    OF    SAND-LIME    ^RICK. 

SILICATE    NO.    8. 

This  sample  was  made  with  3.75  per  cent  CaO  and  fine  crushed  quartz. 
Steamed  for  8  hours  at  12-15  atmospheres. 
Lime-silica  ratio  =.873/1. 
Water-silica  ratio=.726/l. 
Calculated  chemical  formula=8CaO.Si02.7H20. 

silicate  no.   9. 

This  sample  was  made  with  7.5  per  cent  of  CaO  and  the  fine  crushed 
quartz.  It  was  steamed,  as  before,  at  12-15  atmospheres.  After  steam- 
ing only  a  trace  of  free  lime  was  left. 

Lime-silica  ratio  =.837/1. 

Water-silica  ratib=.837/l. 

Calculated  chemical  formula=8CaO.Si02.8H20. 

SILICATE   no.   10. 

This  sample  was  made  by  using  8.75  per  cent  CaO  with  the  crushed 
quartz.      It  was   steamed   as   before   at   12-15   atmospheres.      The   free 
lime  found  after  steaming  was  negligible. 
Lime-silica  ratio  =.853/1. 
Water-silica  ratio=.824/l. 

Calculated  chemical  formula=9CaO.Si02.8H20. 
During  the  hardening  of  this  sample,  water  collected  above  the  mate- 
rial in  the  dish  and  on  this  a  crust  was  formed.     The  crust  dissolved 
completely  in  dilute  hydrochloric  acid  and  showed   a  lime-silica  ratio 
of   .908/1. 

SILICATE    NO.    11. 

This  sample  was  made  by  using  15  per  cent  of  lime  with  fine  quartz 
sand.  The  free  lime  was  removed  by  precipitating  with  Fe2Cl6  and 
decanting  flocculent  ferric  hydrate.  The  sample  was  dried  at  101  °,  and 
separated  into  two  parts  (a  fine  and  a  coarse)  by  means  of  sieves. 
Analysis  showed  the  following  results : 

Coarse  Part.  Fine  Part, 

Lime-silica  ratio  =.910/1.  Lime-silica  ratio=.833/l. 

Water-silica  ratio=. 544/1. 

Calculated  chemical  formula=9CaO.Si02.5H20. 

SILICATE    NO.    12, 

Silicate  No.  12  was  made  with  7.5  per  cent  CaO  and  the  fine  sand 
prepared  from  Ottawa  Standard  sand.  The  steaming  conditions  were 
the  same  as  before,  12-15  atmospheres  for  8  hours. 

Lime-silica  ratio  =.887/1. 

Water-silica  ratio=.748/l. 

Calculated  chemical  formula=8CaO.Si0..7H.,0. 


CHEMISTRY    OF    SAND-LIME' BRICKS. 


57 


A  portion  of  this  sample  was  ground  with  a  sofl   pestle  in  a  mortar 

bo  as  to  remove  the  binding  material  from  the  sand  "Tains  as  much  as 
possible.  The  part  passing  an  80-mesh  sieve  and  retained  on  one  of 
L20  meshes  was  subjected  to  a  process  of  fractionation  in  a  separating 
funnel  originally  devised  by  llarada1  for  the  separation  of  minerals. 
Thoulet's2  solution  was  used  for  the  separation  and  three  fractions  were 
taken.     Analyses  of  the  heavy  and  light  fractions  gave  these  results: 

Lime-silicate  ratio  of  heavy  fraction=.885/l. 

Lime-silicate  ratio  of  light  fraction  =.830/1. 

silicate  no.  13. 

This  sample  was  made  with  10  per  cent  Ca()  and  the  fine  sand  from 
crushed  quartz.  It  was  steamed  for  8  hours  at  12-15  atmospheres,  dried 
at  101°,  and  then  ground  as  before  with  a  soft  pestle  in  a  mortar.  The 
part  passing  a  120-mesh  and  retained  on  one  of  200  meshes  was  retained 
and  fractioned  with  the  aid  of  the  Thoulet's  solution.  Four  fractions 
were  analyzed.  These  yielded  the  results  recorded,  in  the  following 
table : 

Table  21 — Analyses  of  fractions  separated  from  lime-silicate. 


Fraction. 

Sand— 
Per  cent. 

Solubte  SiO  2— 
Per  cent. 

Lime—  - 
Per  cent. 

Lime-silica 
ratio. 

1         

55 .75 

56.70 

34.65 

1.24 

21.75 
21.95 
32.75 
50.00 

22.57 
21.40 
32.60 

48.76 

1.11  .  1 

2         

1 .04  :  1 

3 

1 .08  :  1 

4 

1 .04  :  1 

SILICATE    NO.    14. 

This  sample  was  made  by  using  three  parts  of  CaO  to  one  of  pre- 
cipitated silica,  mixing  with  enough  water  to  form  a  slurry,  shaking 
well,  and  steaming  for  8  hours  at  15-20  atmospheres.  The  steamed 
mass  was  washed  with  boiled  water  into  a  liter  flask,  some  phenolphthalein 
added  and  the  flask  then  connected  to  a  source  of  hydrogen  sulphide. 
This  gas  combined  with  the  lime  and  formed  a  soluble  sulphide  which 
was  removed  several  times  by  decantation.  The  process  was  continued 
until  there  was  hardly  any  reaction  with  phenolphthalein.  The  lime- 
silica  ratios  found  were: 

First   fraction    (heavy) 1.30/1. 

Second  fraction   (heavy) 1.11/1. 

Third  fraction  (light)' -. 1.13/1. 

The  following  experiments  were  undertaken  for  the  purpose  of  ascer- 
taining whether  there  was  any  more  silica  rendered  soluble  by  a  given 
amount  of  lime  when  used  with  crushed  quartz  than  when  used  with 
the  Ottawa  Standard  sand. 


1  Neues  Jahrbuch  fur  Mineralogie,  18S1,  I,  p.  457. 

2  Idem,  p.  179. 


58 


STUDY    OF    SAND-LIME    BRICK. 


EXPERIMENT    NO.    15. 

Into  each  of  four  platinum  crucibles  were  weighed  exactly  0.5  gram 
of  CaO,  which  was  ignited  over  the  blast  lamp  to  remove  any  traces  of 
C02.that  might  have  combined  with  it.  While  still  hot,  5gr.'of  Ottawa 
sand  were  added  to  two  of  these  crucibles,  and  five  grams  of  the  sand 
prepared  from  the  crushed  quartz  to  each  of  the  other  two.  After 
cooling,  boiling  water  was  added  and  the  lime  and  sand  were  thoroughly 
mixed.  The  lids  were  then  placed  on  the  crucibles  and  they  were  placed 
on  a  porcelain  desiccator  tray  in  the  autoclave,  the  water  in  which  was 
boiling  so  that  all  air  was  excluded.  Steaming  was  continued  for  8 
hours  at  about  20  atmospheres.  Practically  all  the  lime  was  in  combi- 
nation at  the  end  of  the  operation.  Two  of  these  samples  were  used  in 
the  determination  of  soluble  silica,  the  other  two  being  used  for  the 
determination  of  combined  water.  The  results  of  the  analyses  of  the 
products  are  shown  in  the  table: 


Table  22 — Eatios  of  products  of  Experiment  No.  15. 


I     Standard  Ottawa 
sand. 

Crushed  quartz 
sand. 

Lime-silica  ratio 

1.18    :1 

.718  :  1 

1.2CaO.Si02.7H20 

1  15    -1 

Water-silica  ratio 

764  •  1 

Calculated  chemical  formula \ 

1.2CaO.Si02  8H>0 

EXPERIMENT    NO.    16. 

The  results  shown  in  the  following  table  are  from  an  experiment 
exactly  parallel  to  Xo.  15,  except  that  the  amount  of  lime  used  was 
one-fourth  instead  of  one-half  gram. 


Table  23 — Eatios  of  products  of  Experiment  No.  16. 


Standard  Ottawa 
sand. 

Crushed  quartz 
sand. 

1.14    :1 

.689  : 1 

l.lCaO.Si02.7H20 

1.11    :1 

.709  : 1 

l.lCaO.Si02.7H20 

EXPERIMENT    NO.    17. 

The  results  shown  in  the  next  table  are  those  of  an  experiment  which 
differed  from  the  one  just  preceding  only  in  that  the  steam  pressure 
was  10  atmospheres  instead  of  20. 


CHEMISTRY   OF    SAND-LIME   BRICKS.  59 

Table  24 — Ratios  of  products  of  Experiment  No.  11. 


Standard  Ottawa 
sand. 

Crushed  quartz 
sand. 

1 .09    :  1 

.897  :  1 

l.lCaO.Si02.9H20 

1.18   :  1 

1.15    :1 

1.2CaO.Si02.2H20 

Table  2 


5 — Summary  of  results  of  chemical  analyses  of  lime  silicates 
experimentally  produced. 


No 

Composition 
of  mixture 
(approx.). 

Experi- 
ment 
number. 

Steam 
pressure 
in 
atmospheres 
used  in  mak- 
ing 
product. 

Composition  of  product. 

Remarks. 

Alois. 
CaO. 

Mols. 
Si02. 

Mols. 
H20. 

1 

Ca0.9Si02 

Ca0.19Si02... 
Ca0.27Si02... 
Ca0.13Si02... 
Ca0.27Si02... 
Ca0.6Si02--.. 
Ca0.13Si02... 
Ca0.9Si02...- 

Ca0.9Si02 

Ca0.19Si02... 
0aO.19Si0o... 
Ca0.19Si02... 
Ca0.19Si02... 

Ca0.3Si02 

Ca0.3Si02 

3CaO.Si02 

Ca0.9Si02 

Ca0.27Si02... 

Ca0.6Si02 

Ca0.13Si02... 
Ca0.13Si02... 
Ca0.9Si02..-. 

Ca0.9Si02 

Ca0.9Si02 

Ca0.9Si02 

3CaO.Si02 

3CaO.Si02 

3CaO.Si02 

4 

5 

8 

9 
10 
11 
12 
15a 
15b 
16a 
16b 
17a 
17b 

2 

3 

6 

7 

10a 
11a 
12 1 
122 
13 1 

13  2 

133 

13  i 
14 1 

14  2 

143 

12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
19-21 
19-21 
19-21 
19-21 
9-11 
9-11 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
12-15 
15-20 

15-20 
15-20 

0.863 

0.890 

0.873 

0.837 

0.953 

0.910 

0.837 

1.18 

1.15 

1.14 

1.11 

1.09 

1.18 

0.899 

0.870 

0.847 

0.818 

0.968 

0.833 

0.885 

0.839 

1.11 

1.04 

1.08 

1.04 

1.30 

1.11 
1.13 

0.632 
0.50S 
0 .726 
0.837 
0.324 
0.544 
0.748 
0.71S 

2 

3 

4 

5 

6 

8 

9 

0.764 
0.689 
0.709 
0.897 
1.15 

10 

11 

1? 

13 

14 

15 

1G 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

?7 

CaO 

28 

Discussion  of  Analyses. 

Reference  to  the  table  will  show  that  in  the  products  made  by  steaming 
silica  with  lime  or  calcium  hydrate  the  ratios  of  lime  to  silica  are  all  in 
the  neighborhood  of  one.  This  indicates  that  in  the  bonding  material 
of  sand-lime  brick  the  lime  and  silica  are  present  in  nearly  equal  molecu- 
lar proportions,  and  that  the  major  part  of  it  is  doubtless  the  hydrated 
calcium  metasilicate  (CaSi03.H20).  The  variations  from  the  ratio 
of  1  to  1  in  the  experimental  products,  however,  are  greater  than  can 
be  attributed  to  experimental  error,  hence  other  silicates  must  also  have 
been  formed.  It  would  seem  that  with  excess  of  lime  the  orthosilicate 
(Ca2Si04)  might  be  formed,  and  that  with  an  excess  of  available  silica 


GO  STUDY    OF    SAND-LIME   BRICK. 

there  would  appear  a  calcium  disilicate  such  as  CaO(Si02)2.  However, 
there  is  as  yet  no  direct  evidence  as  to  the  number  of  compounds  that 
may  be  produced  by  the  methods  employed.  If  calcium  orthosilicate 
is  a  possible  product,  it  would  be  expected  when  lime  and  precipitated 
silica  are  mixed  in  the  molecular  ratio  of  3  to  1,  as  in  numbers  16,  26, 
27,  and  28.  The  analyses,  however,  do  not  indicate  its  presence.  In 
this  connection  it  must  be  remembered  that  in  an  atmosphere  of  dry 
saturated  steam  it  is  possible  that  such  a  compound  may  be  stable,  while 
when  treated  with  an  excess  of  water,  as  it  is  necessary  to  do  in  order 
to  remove  the  free  lime,  it  may  be  broken  down  by  hydrolysis,  especially 
when  the  free  lime  is  removed  by  converting  it  into  the  sulphide  or 
acetate. 

When  excess  of  silica  is  used  in  the  mixture,  chemical  analysis  of  the 
product  is  difficult  if  not  impossible,  unless  the  silica  is  in  the  form  of 
quartz  grains  of  sufficient  size  to  be  only  slightlv  acted  upon  by  dilute 
alkalies.  In  a  mixture  composed  of  such  sand  grains  with  from  5  to 
20  per  cent  of  lime,  only  the  surfaces  of  the  sand  grains  furnish  avail- 
able silica  for  the  reaction;  consequently,  different  parts  of  the  mixture 
will  have  different  compositions,  and  one  would  expect  several  com- 
pounds to  be  formed.  Now,  if  a  mixture  of  compounds  such  as  this  be 
treated  with  a  large  excess  of  water  to  remove  free  lime,  hydrolysis  of 
the  compounds  begins,  and  as  the  dicalcium  silicate  hydrates  most  easily 
it  doubtless  goes  down  to  the  hvdrated  monocalcium  silicate,  thus: 

Ca2Si04+2H20=CaH2Si04+Ca(OH)2. 
This  reaction  is  one  that  actually  occurs  in  the  setting  of  cement.  It 
is  not  improbable  that  an  anhydrous  dicalcium  silicate  may  be  formed 
to  some  extent  at  high  steam  pressure.  If  so,  when  cooled  and  treated 
with  water  it  will  hydrolyze  as  shown  in  the  equation.  In  practically 
all  of  the  experiments  showing  lime-silica  ratios  lower  than  one  the 
"samples  were  washed  with  a  considerable  quantity  of  water,  and  in  some 
cases  with  the  addition  to  the  water  of  a  little  very  dilute  acid  or 
hydrogen  sulphide  gas.  In  the  samples  9  to  13  this  was  not  clone,  but 
tests  for  free  lime  were  made  on  material  just  as  it  came  from  the  steam 
cylinder. 

The  conclusion  seems  to  be  justified  that  the  ratio  in  which  lime  and 
available  silica  are  present  in  the  mixtures  will  determine  to  some  extent 
the  ratio  of  lime  to  silica  in  the  products  formed  from  them.  Since 
the  proportion  of  lime  and  silica  varies  in  different  parts  of  a  sand- 
lime  brick  mixture  a  number  of  silicates  must  be  present  in  the  bonding 
material,  the  greater  part  of  which,  however,  is  doubtless  the  hyd rated 
metasilicate  with  some  orthosilicate  and  some  disilicate. 

In  the  determination  of  water  the  samples  were  dried  to  constant 
weight  at  100°,  and  ignited  in  the  blast  flame.  The  water  in  combina- 
tion was  found  to  vary  from  about  a  third  of  a  molecule  to  something 
more  than  one  molecule  to  each  molecule  of  silica.  It  is  evidently  held 
with  very  different  degrees  of  tenacity,  and  it  is  quite  possible  that  the 
amount  of  water  which  may  be  in  combination  is  not  constant.  It 
appears  to  decrease  with  increasing  steam  pressures,  as  shown  in  expe- 
riments Nos.   15,  16,  and  17.     This  must  be  taken  to  mean  that  the 


CHEMISTRY    OF    SAND-LIME    BRICKS.  61 

decomposition  pressure  of  some  hydrate  in  the  mixture  is  greater  al 
the  higher  temperatures  employed  than  the  pressure  of  saturated  steam, 
and.  therefore,  there  is  a  loss  of  water  at  the  higher  temperatures. 

Prom  the  facts  at  hand  the  conclusion  appeal's  to  he  justified  that  in 
sand-lime  bricks  made  from  pure  calcium  lime  and  silica  sand  we  have 
a  mass  of  sand  grains  held  together  by  a  bonding  material  which  is  a 
mixture  of  hvdrated  calcium  silicates.  The  molecular  ratio  in  which 
lime  and  silica  occur  is  Dearly  equal  to  unity;  consequently,  the  major 
portion  of  this  material  is  douhtless  the  metasilicate  of  calcium,  hvdrated 
to  a  greater  or  less  extent.  Silicates  having  a  higher  and  lower  calcium- 
silica  ratio  than  one  must  he  present  to  a  certain  extent  to  account  for 
the  variation  in  this  ratio  as  determined  by  analysis.  The  amount  of 
water  in  combination  is  evidently  quite  variable. 

It  is  probable  that  under  the  influence  of  steam  lime  is  able  to  attack 
silica  somewhat  as  follows : 

Ca(OH)2+Si02=CaSi03+H20  or  CaSi03.H20. 
CaSi03+Ca  ( OH)  2=Ca2Si04+H20. 

The  orthosilicate  will  doubtless  hydrolyze  to  some  extent,  as  shown  in 
the  following  equation : 

Ca2Si04+2H20=CaH2Si04+Ca  ( OH )  2. 

One  molecule  of  lime  may  also  attack  two  of  silica  with  the  formation 
of  an  hvdrated  disilicate,  thus: 

"  Ca(OH)2+2SiO,=CaH2Si20G. 

In  the  light  of  their  structural  relations,  these  reactions  appear  as 
follows  : 

/OH  5?  /0N  70x      yOH 

Ga  +     5 1  5*    Ga  5i    =  0  +  H,0    or    Ga        Si 

\)H  "  N07  xOx     xOH 

u  (metasilicate)  (hydrated  metasilicate) 

Then  again : 

/OH  /Ox  ,0N       /Ox 

Ca  t    Ca         Si   =   0  =  Ga  5i  Ga   +    H20      or 

/OH  /0N       /OH  /0N      ^Ov 

Ca  +  Ga.      ,5i  ^   Ga         Si  v      .  Ga  +   Z  H20 

NOH  0  OH  0  0/ 

and,  by  hydrolysis : 

/0N      /0K  0N      /OH  yOh 

CaN       Si«  Ga    +   2H20    ^   Ca        Si  +  Ga 

N0'      X0^  \>'      xOH  ^Oh 

Water  may  now  be  eliminated  from  this  to  regenerate  the  anhydrous 
compound,  thus: 

/°\       /OH  n 


Cav  S 


'  w  \ 


-O-       -OH      =     Ca^0/3i    =     °   +    H2° 


6%  STUDY    OF    SAND-LIME    BRICK. 

Or,  two  molecules  might  lose  a  molecule  of  water  between  them,  thus 
giving  a  double  molecule  with  half  the  amount  of  water: 

0  OH  VQ/       \ 


/\./0H  /Ox  y0  +      H20 

0  OH  n0^      Xqh 

(dicalcium    disilicate) 


HOx          OH 
Si  y 

OH 

r      /      \ 

/ 

Oa           x  0 

+   Ga 

v/ 

\ 

HO         xOH 

OH 

Further,  if  this  double  molecule  should  lose  one  of  its  calcium  mole- 
cules by  hydrolysis,  a  disilicate  would  result  thus: 

Ca^     XSi     -    0 

xo^  ' 
Ox?  +     2HzO     ^ 

(calcium     disilicate) 

It  is  quite  probable  that  all  of  these  reactions  take  place  in  the  steam- 
ing of  sand-lime  bricks,  and  perhaps  others.  The  most  stable  molecules 
formed  are  doubtless  the  simplest  ones;  consequently,  we  would  expect 
to  find  the  mass  of  silicates  composed  largely  of  the  simple  calcium 
hydro  metasilicate.  That  this  is  probably  the  case  is  shown  by  the  fact 
that  the  ratio  of  combined  lime  and  silica  is  nearly  unity.  Varying  the 
ratio  of  lime  to  available  silica  in  the  raw  mixture  will  have  an  effect 
on  the  relative  proportions  in  which  the  compounds  are  formed,  as  will 
also  a  variation  in  the  steam  pressure  on  the  relative  amounts  of  water 
held  in  combination. 

General  Conclusions  as  to  the  Constitution  of  Sand-lime 

Bricks. 

1.  Sand-lime  bricks  made  from  pure  materials  consist  of  sand  grains 
cemented  together  by  a  bonding  substance. 

2.  Aside  from  the  calcium  hydrate  or  carbonate  that  may  be  present, 
this  bonding  material  consists  of  a  mixture  of  at  least  two,  and  most 
likely  three,  calcium  silicates,  some  of  which  are  hydrated. 

3.  The  bulk  of  this  mixture  of  silicates  is  calcium  metasilicate 
(CaSi03  or  CaSi03.H20). 

4.  Other  silicates  which  must  be  present  to  some  extent  are  calcium 
orthosilicate  and  calcium  disilicate,  the  latter  of  which  may  contain  one 
or  more  molecules  of  water  of  hydration. 


63 


THE  PHYSICAL  TEXTURE  OF  SAND-LIME 

BRICKS. 


By  the  aid  of  the  polarizing  microscope,  it  is  possible  to  distinguish 
between  isotropic  and  anisotropic  media.  This  may  be  done  for  sub- 
stances very  finely  divided.  Thus,  it  is  an  easy  matter  to  distinguish 
between  ground  glass  and  ground  quartz  or  powdered  salt  and  powdered 
sugar.  If  the  particles  are  large  enough  to  cover  a  considerable  portion 
of  the  field  of  the  microscope,  one  may  distinguish  further  between 
uniaxial  and  biaxial  crystals  or  crystalline  substances  by  observing  the 
interference  figures  in  converged  light.  This  would  enable  one  to  say 
whether  the  substance  crystallizes  in  either  the  hexagonal  or  tetragonal 
systems,  on  the  one  hand,  or  the  orthorhombic,  monoclinic  or  triclinic 
systems,  on  the  other.  If  the  material  should  occur  in  particles  large 
enough,  it  would  be  possible  to  do  many  other  things,  but  for  very  small 
particles  it  is  not  possible  to  say  more  than  that  a  substance  is  isotropic 
or  anisotropic,  unless  definite  crystals  appear. 

In  order  to  gain  any  light  that  might  be  thrown  upon  the  problem 
in  hand  by  this  .method  of  investigation,  sections  were  prepared  from 
several  brands  of  commercial  sand-lime  bricks,  from  a  small  sand-lime 
brick  block  made  in  the  laboratory,  and  from  small  blocks  made  from 
pure  silica  and  lime.  Slides  were  also  prepared  from  material  made  by 
heating  in  sealed  tubes,  for  about  a  week,  mixtures  of  lime  and  silica 
under  a  pressure  of  120  pounds  per  square  inch. 

The  photomicrographs  of  sand-lime  brick  sections  shown  in  Plate  V 
were  taken  as  viewed  by  polarized  light.  They  show  that  the  bonding 
material  of  a  sand-lime  brick  is  not  transparent  like  the  quartz  grains, 
and,  consequently,  that  if  crystalline  at  all  the  crystals  are  very  small 
and  closely  packed. 

Figure  A  of  plate  YI  is  a  photomicrograph'  of  a  section  prepared  from 
equal  molecular  quantities  of  pure  lime  and  precipitated  silica.  The 
material  was  thoroughly  mixed  by  grinding  in  a  mortar  and  then  sub- 
jected to  very  great  pressure  in  molding.  Two  small  cylinders  one-half 
inch  in  diameter  were  made,  and  these  were  steamed  in  the  usual  way. 
The  fracture  of  the  material  was  conchoidal ;  and  the  lustre,  vitreous. 
The  sections  were  made  as  thin  as  was  consistent  with  the  nature  of  the 
material.  When  examined  between  crossed  nicols,  the  field  was  uniformly 
dark  except  for  small  spots  as  shown  in  figure  A.     When  examined  in 


64  STUDY    OF    SAND-LIME   BKICK. 

plane  polarized  light  without  the  use  of  the  upper  nicol  and  at  a  mag- 
nification of  315  diameters  the  section  had  the  appearance  of  figure  B. 
The  lighter  areas  are  isotropic  and  evidently  must  he  either  a  colloid 
or  an  aggregate  of  crystals  belonging  to  the  isometric  system.  The  light 
points  which  appear  between  crossed  nicols  in  A  are  small  crystals 
which  are  doubly  refracting.  It  was  not  possible  to  make  further 
determination  of  these  doubly  refracting  crystals  owing  to  their  small 
size. 

Larger  particles  of  this  doubly  refracting  compound  were  found  in 
the  material  prepared  as  described  under  silicate  No.  14.  Some  of  this 
after  being  freed  from  uncombined  lime  and  washed  thoroughly  was 
put  into  a  hard  glass  tube  and  sealed.  This  tube  was  then  left  in  the 
steam  bath  for  about  two  weeks.  The  material  was  then  removed, 
washed,  dried  and  mounted  in  Canada  balsam.  Somewhat  larger  crystal- 
line bodies  were  apparent,  but  nothing  showing  a  regular  outline  that 
would  permit  of  the  indentification  of  the  crystal  system.  This  slide 
also  furnished  particles  which  in  converged  light  gave  the  uniaxial  inter- 
ference figure.  Calcium  hydrate  crystallizes  in  the  hexagonal  system 
and  so  does  calcium  carbonate,  but  under  the  conditions  whereby  this 
material  was  prepared  there  is  hardly  a  possibility  that  enough  of  either 
of  these  compounds  could  be  present  to  form  crystals  of  such  size. 

It  would  seem,  then,  from  microscopic  evidence  that  we  are  warranted 
in  saying  that  at  least  two  distinct  crystalline  compounds  are  present  in 
calcium  silicates  formed  at  steam  temperatures.  The  isotropic  crystals 
doubtless  represent  a  compound  occurring  to  some  extent  in  the  bonding 
material  of  sand-lime  bricks,  but  present  in  larger  amounts  in  the  com- 
pounds made  from  lime  and  fine  silica  like  that  from  Southern  Illinois. 
Sections  of  sand-lime  bricks,  and  in  fact  all  the  slides  examined,  show 
small,  highly  doubly  refracting  crystalline  particles  that  are  possibly 
the  zeolitic  materials  observed  by  other  investigators.  The  fact  that 
these  particles  show  the  uniaxial  interference  figure  indicates  that  they 
crystallize  either  in  the  hexagonal  or  in  the  tetragonal  crystal  systems. 


ILLINOIS  STATE  GEOLOGICAL  SURVEY. 


Bull.  No.  18,  Plate  V. 


Thin  sections  of  sand-lime  bricks,   viewed   in   polarized   light. 
White — quartz  grains.     Black — bond. 


G5 


TESTS  OF  SAND-LIME  BRICKS. 


The  value  of  a  brick  for  building  purposes  is  determined  very  largely 
by  the  following  properties: 


-V. — Strength; 

I.     Transverse. 
II.     Crushing. 
B.— Durability : 

I.     Kesistance  to  weather. 
II.     Resistance  to  fire. 
C. — Appearance : 

I.     Character  and  uniformity  of  color. 
II.     Regularity  of  size,   form,  etc. 
D. — Uniformity  of  product. 
At  the  last  meeting  of  the  American  Society  for  Testing  Materials 
its  committee  on  standard  specifications  for  testing  building  and  paving 
bricks  submitted  its   report  on  "Proposed   Standard   Specifications   for 
Testing  Building  Brick."'     Four  tests  are  recognized  and  the  desirability 
of  another    (the  fire   test)    is  mentioned.      The  four  that  were   recom- 
mended are  the  transverse  test,  the  compression  test,  the  absorption  test 
and  the  freezing  and  thawing  test. 

The  committee  recommended  that  the  transverse  test  be  made  on  the 
brick  placed  flatwise  on  a  seven-inch  span  with  the  load  applied  midway 
between  the  two  supports.     The  modulus  of  rupture  (E)  shall  be  calcu- 

3We 

lated  from  the  formula:    E= in  which  W  is  the  lead  at  which  the 

2bd2 
brick  fails,  e  the  distance  between  supports  in  inches,  and  b  and  d  are 
respectively  the  breadth  and  depth  of  the  brick  in  inches. 

The  compression  test  is  to  be  made  on  a  half  brick  laid  flatwise  and 
properly  bedded  in  several  thicknesses  of  blotting  paper  or  felt,  or,  if 
very  irregular,  in  plaster  of  Paris.  The  ultimate  load  at  which  the 
brick  Pails  divided  by  the  area  under  compression  is  taken  as  the  crush- 
ing strength  in  pounds  per  square  inch. 

For  the  absorption  test  bricks  are,  first,  to  be  weighed  dry,  then 
placed  in  warm  water,  removed  after  one-half  hour,  wiped  dry,  and  again 
weighed.  This  process  is  to  be  repeated  at  intervals  of  six  and  forty- 
eight  hours.  The  absorption  is  the  total  gain  in  weighl  divided  by  the 
weigh!  of  the  dry  brick,  recorded  in  per  cents. 

—5  G 


66 


STUDY    OF    SAND-LIME   BRICK. 


For  the  freezing  test  the  bricks  are  to  be  alternately  frozen  and  thawed 
twenty  times,  after  which  they  are  subjected  to  the  transverse  and  com- 
pression tests. 

Sand-lime  bricks  have  been  subjected  to  all  the  above  tests  with  satis- 
factory results.  It  is  true  that  not  all  sand-lime  bricks  have  been  found 
satisfactory,  for  many .  poor  bricks  have  been  put  on  the  market,  and 
some  of  these  have  found  their  way  to  the  testing  laboratory. 

Strength  Tests. 

The  strength  of  properly  made  sand-lime  bricks  is  all  that  is  required 
by  the  specifications  of  the  American  Society  for  Testing  Materials.  As 
the  result  of  a  number  of  tests,  Curfman1  found  the  modulus  of  rupture 
of  sand-lime  bricks  to  be  509,  766,  420,  and  607  for  four  different 
brands.     The  results  of  his  crushing  tests  were  as  follows : 


Table  26 — Results  of  compression  tests  on  sand-lime  bricVs. 
(By  Curfman) 


Reference  number. 

Number  tested. 

Average  ultimate 

crushing 

strength  in 

pounds  per 

square  inch. 

1 

12 
3 
12 
13 

4.344 

2 

6, 123 

3 

2.412 

4 

2,244 

5 

7,300 

6 

15  cubes 
10 

1 
2 

1 
3 

952 

7 

2,943 

8 

4,470 

9 

3,002 

10 

3.147 

11 

3.843 

Some  of  these  tests  were  made  on  bricks  that  were  manufactured  when 
the  industry  was  first  introduced  into  this  country  and  were,  conse- 
quently, not  of  as  good  quality  as  the  bricks  now  being  produced. 

No.  6  was  made  on  cubes  and  probably  ought  not  be  compared  with 
the  other  tests  which  were 'made  on  half  bricks. 

Transverse  and  crushing  tests  were  made  by  ourselves  on  22  samples 
of  each  of  two  brands  of  commercial  sand-lime  bricks.  The  bricks  were 
tested  as  received  and  the  results  are  therefore  probably  considerably 
lower  than  they  would  have  been  had  the  brick  been  dried  at  100° 
before  testing.    The  results  obtained  are  shown  in  the  following  table : 


Technograph,  vol.  XIX,  1905,  p.  72. 


ILLINOIS  STATE  GEOLOGICAL  SURVEY. 


Bull.  No.  18,  Plate  VI. 


Microscopic  sections  of  steamed  lime-silica  mixtures. 


DESTS    ;\    SAND-LIME   BRICKS. 

Table  27— Tests  of  sand-lime  brick 


67 


Brand  A. 

' 

Brand  B. 

No. 

Modulus 

of 

rupture. l 

Crushing 
strength  in 

lbs. 

per  square 

inch. 

No. 

Modulus 

of 
rupture. 

Crushing 
strength  in 

lbs. 

per  square 

inch. 

1 

435 
427 
172 
4S4 
416 
422 
414 

*246 
351 
305 

*302 
383 
405 
375 
423 
475 
432 
4^7 
468 
420 
460 
427 

4,230 
4,340 
4,750 
5,000 
4,040 
4,340 
3,900 

*3,800 
4,000 
3,950 
3,900 
4,600 
3,820 
3,960 
4,850 
4, 750 
4,400 

*5, 140 
4,130 
4,360 
5,000 
3,980 

1 

843 
952 
72S 
662 
675 
605 
957 
700 
*635 
587 
653 
675 
645 
572 
686 

4,420 

2... 

2 

4,000 
3,980 

3... 

3 

4 

4... 

2,880 

5 

*2, 440 

6 

6 

2,950 

7 

3,800 

8 

8: 

3.540 

9 

9 

2,790 

10 

10 

*2, 490 

11 

11 

3,570 
3,460 
2,750 

12... 

12 

13... 

13 

14.    . 

11 

3,060 
3  620 

15 

15 

16 

16 

3,020 

17 

17 

761 
700 
806 
723 
661 
743 

3,540 

18 

18 

2,780 

19 

19 

4,300 

20 

20 

3.900 

21 

21 

3.360 

22 

22 

Mean 

3,490 

Mean 

420 

4.320 

720 

3.470 

Effects  of  Freezing  Bricks. 

The  ability  of  any  material  to  withstand  the  action  of  the  weather 
will  depend  very  largely  on  the  amount  of  water  it  will  absorb.  If  only 
a  little  water  is  taken  up  (5-10%)  this  will  be  held  very  largely  by 
the  capillarity,  and  it  will  not  segregate  to  form  ice  crystals  when 
frozen,  while  if  more  water  is  taken  up,  freezing  will  cause  ice  crystals 
to  form  within  the  body  of  the  brick  and  wedge  its  particles  apart. 
Sand-lime  bricks  can  be  made  with  absorption  as  low  as  5  per  cent,  but 
this  is  expensive  and  undesirable,  since  about  8  per  cent  of  absorption 
is  needed  to  dry  the  mortar  used  in  laying  the  bricks  and  make  it  stick. 
Brick  with  10  per  cent  absorption  can  easily  be  made,  and  this  should  be 
the  goal  toward  which  the  manufacturer  should  work.  As  has  been  said 
before,  the  bonding  material  in  sand-lime  brick  is  the  real  absorbing- 
constituent;  consequently,  if  the  absorption  is  too  high,  the  quantity  of 
bond  made  should  be  reduced  by  decreasing  the  ratio  of  fine  or  dust-like 
constituent  in  the  mixture.  The  following  table  showing  the  effect  of 
freezing  on  brick  is  quoted  from  Curfman's  article   (loc.  cit.). 


1  First  eleven  tests  were  made  on  bricks  placed  edgewise. 
*  These  tests  are  not  included  in  the  means. 


68 


STUDY    OF    SAND-LIME    BRICK. 


Table  28 — Effect  of  freezing  on  crushing  strength  and  absorption   of 

sand-lime   bricks. 


Reference 

Private 
mark. 

Number 

tested. 

Absorption — Per  cent  by 
weight. 

Average  crushing  strength— Pounds 
per  square  inch. 

mark. 

Before 
freezing. 

After 
freezing. 

Before 
freezing. 

After 
freezing. 

Loss  in 
weight. 

1 

2 

C 

Cs 

4 
2 
6 

10.85 
8.80 
13.10 

14.25 
9.20 
14.97 

4,448 
6,  200 
2,470 

3,430 
6,225 

1,778 

Not  found 
Not  found 

3 

U 

14.20 

It  will  be  noted  that  the  brick  which  was  strongest  after  freezing  was 
•the  one  possessing  the  lowest  absorption. 


09 


FIRE  RESISTING  QUALITIES  OF  SAND-LIME 

BRICKS. 


The  effect  of  fire  on  sand-lime  bricks  has  attracted  a  great  deal  of 
attention,  and  it  is  a  question  of  considerable  importance.  The  condi- 
tion, of  the  walls  of  a  building  that  has  burned  is,  in  some  cases,  a 
matter  of  thousands  of  dollars.  Many  investigations  have  been  under- 
taken for  the  purpose  of  studying  this  property,  but  most  of  them  have 
been  of  a  qualitative  nature  only. 

Curfman  constructed  a  small  house  or. kiln  of  the  bricks  to  be  tested, 
and  in  this  he  built  a  wood  fire  which  was  kept  burning  for  a  little 
more  than  half  an  hour.  The  bricks  were  then  removed  and  tested  for 
soundness  by  blows  with  a  stick,  and  for  crushing  strength.  Again  in 
another  test,  he  dashed  the  previously  heated  walls  Avith  cold  water,  and 
studied  the  effects.  In  still  another  experiment  he  placed  several  half 
bricks  on  the  traveling  gate  of  an  automatically  stoked  boiler  and 
allowed  them  to  pass  through  the  fire  box.  In  none  of  these  experi- 
ments was  any  attempt  made  to  determine  the  temperature  to  which 
the  bricks  were  subjected,  but  it  is  safe  to  assume  that  it  was  in  the 
neighborhood  of  1000°  C.  in  the  last  experiment.  At  high  temperatures 
the  bond  was  found  to  be  destroyed. 

The  effect  of  fire  on  a  sand-lime  brick  wall  was  studied  at  the  Under- 
writers Laboratory,  Chicago,  by  Eichard  L.  Humphrey,1  who  constructed 
a  furnace  having  one  side  closed  with  a  panel  built  of  the  material  to  be 
tested.  Temperatures  were  carefully  measured  both  inside  the  furnace 
and  at  the  back  of  the  wall.  During  the  test  made  with  sand-lime 
bricks  the  wall  bulged  considerably  toward  the  fire.  After  firing  40 
minutes,  the  faces  of  the  bricks  next  the  fire  had  a  chalky  appearance, 
as  though  the  lime  were  dehydrated,  and  when  quenched  with  water 
after  a  two-hours  fire,  the  bricks  spalled  off  to  an  average  depth  of  about 
half  an  inch.  Some  of  the  bricks  were  removed  from  the  panel  and 
tested  for  strength,  absorption,  etc.  The  result-  of  these  tests  are  shown 
in  the  table  below : 


'  Bull.  U.  S.  Geol.  Survey,  No.  370,  1909,  p.  77. 


70 


STUDY    OF    SAND-LIME    BRICK. 


Table  29 — Physical  properties  of  sand-lime  brick  before  and  after  firing. 
(By  E.  L.  Humphrey) 


Normal. 

Immersed   in   water 
for  48  hours . 

Water  absorption. 

Transverse  strength. 

Com- 
pressive 
strength 

per 
square 
inch. 

Com- 
pressive 
strength 

per 
square 
inch. 

Re- 
duction 

in 
com- 
pressive 
strength. 

30  min- 
utes. 

4 
hours. 

Breaking 
load. 

Modulus 
of  rup- 
ture. 

48 
hours. 

Not  fired 

Pounds. 

[         913 
909 

\          797 
|          684 
I          695 

364 
362 
318 
273 

277 

Pounds. 
2,020 
2,510 
2,161 
1,923 
1,562 

Pounds. 
1,816 
1, 636 
1,604 
1,382 
963 

Per  cent. 
10.1 
34.8 
25.8 
28.1 
38.3 

Per  cent. 
16.33 
16.30 
9.81 
18.22 
13.04 

Per  cent. 
16.59 
16.60 
13.62 
18.29 
13.91 

Per  cent. 
16.59 
16.60 
13 .62 

18.29 
14.28 

Average 

800 

319 

2,035 

1,480 

27.4 

14.74 

15.80 

15.88 

Brick  from  back  of 
wall 

f         642 
841 

\          770 

789 

1         645 

256 
336 
308 
315 

258 

2,117 
2,109 
1,208 
2,430 
1,790 

1,261 

976 

1,451 

1,468 

873 

40.5 
53.7 
*20.0 
39.6 
52.2 

15 .30 
11.90 
13.72 
13.80 
16.92 

15.3 

13.45 

15.79 

14.30 

16.92 

15.3 

14.00 

15.79 

14.30 

16.92 

Average 

737 

295 

1,931 

1,206 

33.2 

14.33 

15.15 

15.26 

Brick    with    ends 
exposed 

f         494 
756 
707 
463 

(         551 

197 
302 
282 
185 
220 

1,952 
2,176 
2,109 
1,306 
1,541 

1,189 
826 
1, 157 
1,444 
1,289 

39.1 

62.0 

45.0 

*10.5 

16.4 

14. G5 
12.30 
13.90 
12.00 
10.40 

14 .65 
13.20 
13.90 
13.80 
12.87 

14.65 
13  .20 
13.90 
13  .80 

12.87 

Average 

594 

237 

1,817 

1,181 

30.4 

12.65 

13.68 

13.68 

r 

1,112 
1,794 
1,827 
1,994 
2,024 

838 
1,384 

902 
1,270 
1,536 

24.7 
22.8 
50.6 
36.3 
24.1 

19.11 
12.70 
18.50 
16.60 
12.82 

19.30 
13.91 
18.80 
16.60 
13.83 

19 .30 

Brick  with  face  ex- 

14.17 

posed 

127 
117 

[          126 

58 
53 
58 

18.80 

16.91 
14.21 

Average 

123 

56 

1,750 

1,186 

31.7 

15.95 

16.49 

16.68 

Theory  would  lead  to  the  conclusion  that  at  about  red  heat  the  water 
of  hydration  is  driven  out  of  the  sand-lime  bricks,  thus  partly  destroying 
the  hydrated  silicate  bond.  If  high  enough  temperatures  are  reached, 
however,  the  recombination  of  the  lime  and  silica  might  take  place  with 
the  formation  of  an  anhydrous  calcium  silicate  bond,  in  which  case  a 
true  silica  brick  would  result.  It  was  with  the  intention  of  testing  this 
theory,  and  also  of  studying  the  effect  of  various  degrees  of  heat  on  the 
strength  of  sand-lime  bricks,  that  the  experiment  described  below  was 
carried  out. 

Description  of  Methods  of  Testing  Fire  Resistance. 


MATERIALS   USED    IN   TESTS. 


The  materials  used  in  this  experiment  were  two  brands  of  commercial 
sand-lime  bricks  sent  at  our  request  by  the  manufacturer.  There  could 
have  been  no  selection  made  at  the  factorv  other  than  the  exclusion  of 


Increase. 


I'IKi:   TESTS   OE   SAND-LIME  BEICKS.  71 

chipped  or  cracked  specimens.  More  bricks  were  ordered  than  were 
actually  required  for  the  test,  and  only  those  free  from  cracks,  checks, 
etc.,  were  used. 

APPARATUS   USED  IN   TESTS. 

The  kiln  used  for  burning  is  one  belonging  to  the  Department  of 
Ceramics  of  the  University  of  Illinois.  It  is  of  the  down-draught  type 
and  has  a  capacity  of  150  bricks.  The  first  gases  pass  up-  the  back, 
then  down  through  the  ware,  up  in  front,  and  over  the  top  to  the  flue. 
Connellsville  coke  was  used  for  fuel,  and  temperatures  were  measured 
by  the  use  of  a  thermo-electric  couple  of  the  platinum-rhodium  type. 
The  couple  was  enclosed  in  a  quartz  glass  tube  which  was  inserted  into 
a  fire  clay  tube  set  in  the  kiln.  The  crushing  and  cross-breaking 
strengths  of  the  heated  bricks  were  tested  in  two  100,000-pound  Riehle 
testing  machines  belonging  to  the  Laboratory  of  Applied  Mechanics  of 
the  same  University.  These  are  exactly  alike,  except  that  on  the  slow 
speed,  one  advances  at  the  rate  of  1/5  inch  per  minute,  while  the  other 
is  geared  to  move  only  half  as  fast.  The  latter  of  these  was  used  for 
the  transverse  tests, 

BURNING   TESTS. 

The  procedure  in  burning  was  as  follows :  The  bricks  were  set  in  the 
kiln,  the  fire-clay  pyrometer  tube  was  put  in  place,  and  a  wicket  was 
built  up  on  the  evening  preceding  the  firmer.  The  fire  was  started  and 
about  three  or  four  hours  were  taken  to  bring  the  temperature  up  to 
300°,  when  the  first  draw  was  made.  The  heat  was  then  slowly  increased 
and  drawings  of  11  bricks  were  made  at  each  100°  rise  in  the  tempera- 
ture, until  the  maximum  temperature  was  reached  at  the  end  of  about 
20  hours.  When  drawn,  the  bricks  were  allowed  to  cool,  and  were 
marked  and  carefully  packed  so  as  not  to  be  injured  in  being  removed 
to  the  laboratory  where  the  tests  were  made.  The  burns  at  1370°  and 
1290°  were  made  at  a  later  time  in  connection  with  some  clay  tests. 
The  temperature  was  measured  at  this  time  by  the  use  of  Seger  cones, 
Xos.  12  and  8  being  the  limits  to  which  firing  was  carried. 

TESTING. 

The  tests  were  made  according  to  the  latest  specifications  of  the 
American  Society  for  Testing  Materials  (Eeport  of  Committee  at  Atlan- 
tic City  Meeting,  July,  1909;  published  in  Proceedings,  Vol.  IX.),  which 
reads,  in  part,  as  follows: 

"Transverse  Test. — At  least  five  bricks  shall  be  tested,  laid  flatwise 
with  a  span  of  7  inches,  and  with  the  load  applied  at  middle  span.  The 
knife  edges  shall  be  slightly  curved  in  the  direction  of  their  lengths. 
Steel  bearing  plates,  about  one-half  inch  thick  and  iy2  inches  wide,  may 
be  placed  between  the  knife  edges  and  the  brick.  The  use  of  a  wooden 
base-block,  slightly  rounded  transversely  across  its  top,  upon  which  to 


72 


STUDY    OF    SAND-LIME    BRICK. 


rest  the  lower  knife  edges,  is  recommended.     The  modulus  of  rupture 

3We 

shall  be  obtained  by  the  following  formula :    R= in  which  e  is  the 

2bd2 
distance  between  supports  in  inches,  b  is  the  breadth  and  d  the  depth 
of  the  brick  in  inches,  W  is  the  load  in  pounds  at  which' the  brick  failed. 
"Compression  Test. — Compression  tests  shall  be  made  on  Half  bricks 
resulting  from  the  transverse  tests.  The  bricks  shall  be  bedded  flatwise 
on  blotting  paper,  heavy  fibrous  building  paper,  or  felt,  to  secure  a 
uniform  bearing  in  the  testing  machine.  *  *  *  The  machine  used 
for  compression  tests  shall  be  equipped  with  spherical  bearing  blocks. 
The  breaking  load  shall  be  divided  by  the  area  in  compression,  and  the 
results  reported  in  pounds  per  square  inch." 

METHOD   OF    AVERAGING    RESULTS. 

The  result  of  each  individual  test  was  recorded,  but  before  taking 
their  mean,  one  out  of  every  eleven  was  discarded.  The  object  was,  of 
course,  to  eliminate  any  test  that  was  noticeably  out  of  accord  with 
the  others.  In  the  case  of  the  transverse  tests  there  were  several 
instances  in  which  more  than  10  per  cent  had  to  be  discarded  before 
taking  the  mean.. 

DISCUSSION    OF    RESULTS. 

The  results  of  the  tests  are  shown  graphically  in  figures  3  and  4,  in 
which  temperatures  in  hundreds  of  degrees  centigrade  are  represented 


Ser/eS  A 

7 
Ser/es  3 

/ 

P 

// 

£3*00 

/ 

^ 

\ 

f 

is)*000 

\ 

t-      g 

\ 

r>       ( 

rushing 

vo 

Fig.   3. 


7~emperature    in  hundred  degrees    C. 


Curves   recording  crushing  strength  of  sand-lime  bricks  heated  to 
different   temperatures. 


FIRE   TESTS    OF   SAND-LIME    BRICKS.  76 

as  abscissas,  and  pounds  pressure  as  ordinates.  The  two  curves  in 
figure  3  show  the  reaction  between  crushing  strength  and  temperature, 
and   the  two   in    figure    I   show  the  effecl   of  heat  on    the   modulus  of 

rupture.  It  will  be  noticed  that  the  modulus  of  rupture  falls  off  con- 
tinuously  until    1100°    is   reached,   and   then   begins   to   increase.      The 


iTe  m  pe  r  af  u  r  e 


7         8         9        /o       //        /2       /s 
in  hu  ndred  degrees  C 


/5 


Fig.    4.     Curves    recording   variations    in    modulus    of   rupture    of    sand-lime 
bricks  heated  to  different  temperatures. 


curves  recording  compressive  strength,  on  the  other  hand,  show  a  marked 
increase  at  300°.  This  can  probably  be  explained  on  the  supposition 
that  at  this  temperature  the  bricks  are  more  thoroughly  dried  than  at 
lower  temperatures,  and  that  any  combined  lime  originally  present  in 
them  is  changed  to  the  carbonate  by  the  fire  gases.  At  500°  the  curves 
have  a  minimum  which  has  not  as  yet  been  satisfactorily  explained.  It 
is  known,1  however,  that  at  570°  quartz  undergoes  quite  a  sudden  change 
in  volume,  and  this  may  explain  the  phenomenon. 

The  gradual  fall  in  strength  from  500°  to  900°  is  probably  brought 
about  by  a  number  of  causes.  First,  after  passing  600°  water  doubtless 
begins  to  come  off  quite  rapidly;  second,  any  calcium  carbonate  that 
has  been  formed  will  be  decomposed  between  these  limits;  third,  at  800° 
we  have  the  point  beyond  which  quartz  ceases  to  be  the  stable  form  of 
silica  and  an  inversion  into  tridymite  begins.  This  inversion  is  accom- 
panied by  a  marked  increase  in  volume  which  is  very  detrimental  to  the 
bond.  The  final  increase  in  both  compression  and  transverse  strength- 
is  easily  explained  by  the  fact  that  here  there  is  a  combination  of  lime 
and  silica  to  form  a  bond  of  anhydrous  calcium  silicate. 


Compt.  Rendu,  vol.  103,  1889,  p.  104(1  and  vol.  109,  1889.  p.  264.    See  also  page  16  of  this  paper. 


74. 


STUDY    OF    SAND-LIME   BRICK. 


The  results  of  the  tests  indicate  that  the  compressive  strength  of  sand- 
lime  bricks  will  be  diminished  only  slightly  by  any  ordinary  conflagra- 
tion. Their  transverse  strength,  however,  diminishes  at  a  rate  very  nearly 
proportional  to  the  temperature,  especially  for  low  temperatures.  It 
may  be  said  in  favor  of  sand-lime  bricks,  however,  that  in  all  the  speci- 
mens tested  there  was  not  a  sign  of  warping  or  shrinkage  except  at  the 
highest  temperature,  where  some  of  the  samples  cracked  and  warped 
badly.  In  nearly  every  instance  of  this  kind  there  was  found  a  lump  of 
lime,  in  some  cases  of  considerable  size,  which  probably  was  the  cause 
of  the  fracture.  At  1200°  the  bricks  had  a  very  pleasing  appearance, 
resembling  very  much  a  high  grade  buff  face  brick.  In  the  tests  for 
transverse  strength  the  unburned  bricks  and  those  heated  to  the  highest 
temperature  broke  with  a  snap;  at  all  other  temperatures  the  failure 
could  be  detected  only  by  the  drop  in  the  scale  beam.  At  the  highest 
temperatures  reached,  and  also  at  500°  in  the  case  of  one  series,  when 
subjected  to  the  compression  test  the  specimens  failed  with  a  crashing 
sound,  resembling  in  this  respect  vitrified  clay  bricks. 

Conclusions  Kegarding  Fire  Eesistance. 

It  has  been  shown  that  the  effect  of  heat  on  the  strength  of  sand-lime 
bricks  is  a  function  of  the  temperature  reached.  It  is  not  probable 
that  in  an  ordinary  conflagration,  the  temperature  often  goes  high 
enough  to  result  in  the  formation  of  a  true  silica  brick;  so  that  in 
considering  sand-lime  bricks  from  the  standpoint  of  their  ability  to 
pass  with  immunity  through  conflagrations  only  the  first  halves  of  the 
curves  need  to  be  considered.  In  any  final  conclusions  as  to  the  relative 
merits  of  sand-lime  bricks  as  compared  with  other  bricks,  it  must  be 
remembered  that  strength  is  but  one  of  many  properties  to  be  consid- 
ered, and  that  in  the  matter  of  conductivity,  shrinkage,  coefficient  of 
expansion,  warping,  etc.,  sand-lime  bricks  behave  very  well. 

Table  30 — Fire  tests  on  sand-lime  bricks. 


Series  A.. 

Series  B. 

Temperature- 
Degrees 
C. 

Modulus 

of 
rupture. 

Compressive 
strength 

lbs. 

per  square 

inch. 

Temperature- 
Degrees 
C 

Modulus 

of 
rupture. 

Compressive 
strength, 

lbs. 

per  square 

inch. 

000 

430 
238 
145 
95 
83 
68 
68 
33 
33 
26 
47 
131 
554 

4,382 
4. 980 
4. 650 
3^720 
4,440 
4, 155 
3,130 
2,050 
2,440 
2,350 
1,310 
2,250 
3,341 

ooo...: 

300 

717 

418 

388 

197 

142 

100 

116 

85 

61 

37 

101 

210 

157 

3,430 

300                   

3,900 
3,710 
3,340 

400 

400 

500 

500 

600 

600 

3,320 

700 

700 

2,640 

800 

800 

2,400 

900 

900 

1,700 

1000 

1000 

1.680 

1100 

1100 

1,280 

1200 

1200 

1,670 

1290 

1290 

1370 

2,505 

1J70 

4,860 

SUMMARY. 


In  appearance,  sand-lime  bricks  are  very  pleasing.  Their  color  varies 
from  a  pure  white  to  a  dark  gray.  Where  colored  sands  are  used  in 
mixtures  from  which  they  are  made,  brown,  red  and  other  colored  bricks 
may  be  produced.  The  bricks  may  also  be  colored  by  an  admixture  of 
various  kinds  of  coloring  matter,  or  by  precipitating  coloring  material 
within  their  pores.  In  cases  where  artificial  coloring  is  to  be  practiced, 
it  is  essential  that  the  sand  used  in  making  the  bricks  be  of  such  a 
character  as  not  to  interfere  with  the  color.  It  should,  preferably,  be 
fine  and  white. 

Sand-lime  bricks  are  very  uniform  in  size  and  shape.  They  are  larger 
than  the  ordinary  clay  bricks  owing  to  the  fact  that  they  do  not  shrink 
on  hardening,  and  therefore  fewer  are  needed  for  the  construction  of  a 
given  mass  of  masonry.  Again  less  mortar  is  required  in  laying  the 
sand-lime  bricks  because  of  their  regular  shapes,  and  masons  can  work , 
more  rapidly  with  them  because  no  time  is  required  to  select  the  best 
face  for  the  outside  of  the  wall. 

From  a  careful  consideration  of  all  information  at  hand,  the  conclu- 
sion seems  to  be  warranted  that  sand-lime  bricks  have  successfully  with- 
stood every  reasonable  test  required  of  them,  and  that  the  future  of  the 
industry  in  this  country  is  assured.  Replies  received  to  circular  letters 
sent  out  to  the  trade  show  that  most  manufacturers  are  prospering  and 
that  the  prejudice  always  found  to  exist  against  a  new  building  mate- 
rial is  being  gradually  removed.  . 

The  future  of  the  industry  demands  that  a  good,  reliable  product  be 
put  upon  the  market  and  at  a  reasonable  price.  In  order  that  this  may 
be  done,  it  is  essential  that  care  be  exercised  in  the  location  of  manu- 
facturing plants.  The  prospect  of  securing  a  ready  market  and  of 
having  at  hand  an  abundant  supply  of  good  sand  should  weigh  heavily 
in  the  final  selection  of  a  site. 

The  character  of  the  sand  should  be  taken  into  consideration  in  the 
selection  of  the  process  to  be  used  in  the  preparation  of  the  mixture  of 
sand  and  lime.  For  the  sake  of  economy  in  the  use  of  lime,  and  in 
order  to  promote  strength,  and  to  reduce  absorption  in  the  finished 
bricks,  the  percentage  of  bonding  material  should  not  be  very  much 
in  excess  of  that  required  to  unite  thoroughly  the  sand  grains  into  one 
compact  mass;  or,  in  other  words,  should  be  just  enough  to  fill  the 
voids  in  a  properly  proportioned  mixture  of  fine  and  coarse  sands. 


76  STUDY    OF    SAND-LIME    BRICK. 

It  has  been  shown  that  the  bond  of  a  sand-lime  brick  is  a  mixture  of 
silicates  of  calcium,  and  that  the  simple  calcium  metasilicate  or  hydro- 
metasilicate  (CaSi03  or  CaSi03.H20)  is  the  principal  compound  of 
this  mixture.  Other  silicates,  as  stated  on  page  59,  must  also  be  pres- 
ent in  small,  variable  amounts,  dependent  on  the  conditions  of  manu- 
facture of  the  bricks. 

Sand-lime  bricks  have  repeatedly  passed  satisfactorily  all  the  tests 
recommended  for  building  bricks  by  the  American  Society  for  Testing 
Materials.  The  effect  of  heat  upon  them  has  been  shown  to  depend 
upon  the  temperature  to  which  they  are  subjected,  a  red  heat  causing 
the  bond  to  break  up,  while  a  white  heat  causes  recombination.  Enough 
work  has  been  done  along  this  line  to  warrant  the  statement  that  for 
all  ordinary  purposes  sand-lime  bricks  afford  a  safe  and  reliable  build- 
ing material. 


;; 


BIBLIOGRAPHY. 


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brick: 

Genie  Civil,  vol.  38,  1900,  p.  77. 

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Tonind.  Zeit.,  vol.  24,  1900,  p.  1812. 

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in  use: 

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8.  H'enschke  &  Niemer,  Feuerwerkung  auf  Kalksandsteine: 

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21.  Paul  Tafel,  Early  history  of  the  sand-cement  and   sand-lime  brick   in- 

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78  STUDY    OF    SAND-LIME    BRICK. 

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25.  Siloverfaren  fur  Kalksandsteine: 

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26.  S.  V.  Peppel,  Dampferhartung  und  Festigkeit  der  Kalksandsteine: 

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27.  M.  Glasenapp,  Theorie  der  Kalksandsteinerhartung: 

Tonind.  Zeit.,  vol.  28,  1904,  p.  1164. 

28.  M.  Glasenapp,  Weitere  Untersuhucngen  uber  Kalksandsteine: 

Tonind.  Zeit.,  vol.  28,  1904,  p.  383. 

29.  A.  Maiston,  Tests  of  sand-lime  and  concrete  building  blocks: 

Eng.  News,  vol.  51,  1904,  p.  387. 

30.  Daniel  P.  DeLong,  Sand-lime  brick  from  the  brickmaker's  point  of  view: 

Am.  Arch.,  vol.  84,  1904,  p.  23. 

31.  E.  Schleier,  Herstellung  der  Kalksandsteine: 

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32.  M.    Glasenapp,    Einflusz    des    Feinsandzusatzes    zur    Kalksandsteinmis- 

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33.  R.  F.  Oswald,  Das  Harten  der  Kalksandsteine: 

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34.  G.  Beil,  Sind  Kalksandsteine  feuersicher? 

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35.  E.   Schleier,  Frostproben  mit  Kalksandsteinen: 

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36.  H.  B.  Fox,  A  comparative  study  of  sand-lime  and  clay  brick: 

Clay  Worker,  vol.  43,  1905,  p.  73. 

37.  L.  E.  Curfman,  Tests  of  sand-lime  brick:. 

Technograph,  vol.  19,  1905,  p.  72. 

38.  Rudolph  Seldis,  Der  Harteprozesz  in  der  Kalksandsteinfabrikation: 

Zeit.  angew  Chem.,  vol.  19,  1906,  p.  181. 

39.  E.  W.  Lazell,   Sand-lime  brick    (Manufacture,  Tests,  etc.) : 

Eng.  Min.  Jour.,  vol.  81,  1906,  p.  397.     . 

40.  Ira  H.  Woolson,  Tests  of  strength  and  fireproofing  qualities  of  sand-lime 

brick: 

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41.  Description  of  plant  at  South  River,  New  Jersey: 

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gone: 

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43.  A.   B.     The  manufacture  of   silico   calcareous  brick,   description   of  the 

Rohrig-Konig  process: 

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44.  E.  Cramer,  Uber  die  H'artung  von  Kalksandsteine: 

Tonind.  Zeit.,  vol.  30,  1906,  p.  635. 

45.  Fr.  Sprotte,  Kalksandsteine  im  Feuer: 

Tonind.  Zeit.,  vol.  30,  1906,  p.  2199. 

46.  E.  W.  Lazell,  Sand-lime  brick,  their  manufacture,  materials  and  uses: 

Proc.  Eng.  Club  of  Phil.,  vol.  23,  1906,  p.  1. 

47.  The  constitution  of  sand-lime  brick: 

Mineral  Resources  for  1906,  U.  S.  Geol.   Survey,  1907,  p.  991. 

48.  R.  Seldis,  Uber  die  Chemie  der  Kalksandsteine: 

Tonind.  Zeit.,  vol.  30,  1906,  p.  637. 


BIBLIOGRAPHY.  79 

49.  The  manufacture  and  use  of  sand-lime  brick: 

Municipal  Eng.,  vol.  32,  1907,  p.  4. 

50.  E.  W.  Smythe,  A  review  of  the  history  of  sand-lime  brick  and  its  uses: 

Sci.  Am.  Suppl.,  vol.  63,  1907,  p.  26239. 

51.  H.  Seger  und  E.  Cramer,  Quartz  als  Rohstuff  fur  Kalksandstein: 

Tonind.  Zeit,  vol.  31,  1907,  p.  1873. 

52.  Der  Einflus  des  hydraulischen  Kalkes  auf  den  Kalksandstein: 

Tonind.  Zeit.,  vol.  31,  1907,  p.  1605. 

53.  Edward  Eckel,  The  Chemistry  of  Sand-Lime  Brick: 

Rock  Products,  vol.  7,  1907,  p.  49. 

54.  E.  Schleier,  Festigkeitszunehme  von  Kalksandsteine: 

Tonind.  Zeit.,  vol.  32,  1908,  p.  871. 

55.  E.  W.  Lazell,  Physical  properties  of  sand-lime  brick: 

Municipal  Eng.,  vol.  34,  1908,  p.  307. 

56.  Otto  Bottcher,  Miszfarbung  von  Kalksandsteine: 

Tonind.  Zeit.,  vol.  32,  1908,  p.  728. 

57.  M.  Glasenapp,  Verfahren  der  Herstellungen  einer  farbigen  Oberflachen- 

schrucht  auf  Kalksandsteine: 

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58.  Fred  Weingart,  Hydraulischer  Kalk  fur  Kalksandsteine: 

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Proc.  Eng.  Soc.  of  Indiana,  vol.  29,  1909,  p.  86. 

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80 


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81 

Waters  of  Illinois,  by  J.  A.  Udden.  Boiler  Waters,  by  S.  W.  Parr.  Medicinal 
Springs  of  Illinois,  by  Dr.  George  Thomas  Palmer.  Gratuitous  edition  ex- 
hausted.    Sale  price  25  cents. 

Bulletin  11.  The  Physical  Features  of  the  Des  Plaines  Valley:  by  James 
Walter  Goldthwait.  Geography  and  History  of  the  Des  Plaines  Valley. 
Structure  of  Bed  Rock.  Deposition  of  Paleozoic  Sediments.  Glacial  and 
Inter-Glacial  Deposits.  Physiographic  History  of  the  Upper  Des  Plaines 
River.  Floods  on  the  Des  Plaines  River.  103  pages,  9  plates,  21  figures. 
Postage  6  cents. 

Bulletin  12.  Physiography  of  the  St.  Louis  Area:  by  N.  M.  Fenneman.  An 
educational  bulletin  describing  the  physiographic  and  geologic  features  of  the 
region  and  including  a  colored  geological  map  of  the  area.  This  is  especially 
designed  to  meet  the  needs  of  teachers  in  the  public  schools.  81  pages, 
18  plates,  10  figures.     Postage  6  cents. 

Bulletin  13.  The  Mississippi  Valley  between  Savanna  and  Davenport: 
by  J.  Ernest  Carman.  A  popular,  yet  scientific  treatment  of  the  physiographic 
and  geologic  features  of  the  region  and  including  two  colored  geological  maps 
of  the  area.     96  pages,  21  plates,  26  figures.     Postage  8  cents. 

Bulletin  Uf.  Year  Book  for  1908:  by  H.  Foster  Bain,  director,  and  others. 
Including  administrative  report;  report  of  the  topographic  survey  of  Illi- 
nois; studies  of  Illinois  coals;  coal  deposits  and  possible  oil  field  near  Du- 
quoin;  papers  on  artificial  silicates  with  reference  to  amorphous  silica;  nat- 
ural gas  in  glacial  drift,  Champaign  county;  paleo-botanical  work;  proceed- 
ings  of   Illinois   Fuel   Conference.     394  pages,   5   plates,   5   figures.     Postage 

13  cents. 

Bulletin  15.  Geography  of  the  Middle  Illinois  Valley:  by  Harlan  H.  Bar- 
rows. An  educational  bulletin,  which  will  give  teachers,  as  well  as  general 
readers,  a  clearer  understanding  of  the  geography  and  history  of  this  inter- 
esting region.     128  pages,  16  plates,  47  figures.     Postage  8  cents. 

Bulletin  16.  Year  Book  for  1909:  by  Frank  W.  DeWolf,  director,  and  others. 
This  publication  includes  papers  on  oil,  coal,  lead  and  zinc,  stratigraphy,  and 
report  of  progress  of  topographic,  geologic,  and  drainage  surveys.  400  pages, 
37  plates,,  and  9  figures.     Gratuitous  edition  exhausted.     Sale  price  40  cents. 

Available  Separates. 
From  Bulletin  8. 

8c.  Artesian  Weils  in  Peoria  and  Vicinity:  by  J.  A.  Udden.  20  pages,  1 
plate,  1  figure.     Postage  2  cents. 

8d.  Cement  Making  Materials  in  the  Vicinity  of  La  Salle:  by  Gilbert  H. 
Cady;  together  with,  Concrete  Materials  produced  in  the  Chicago  District: 
by  Ernest  F.  Burchard,  a  reprint  from  U.  S.  Geological  Survey  Bulletin  340. 
33  pages,  1  plate,  1  figure.     Postage  2  cents. 

8f.  Clay  Industries  of  Illinois,  Statistics  and  Directory:  by  Edwin  F. 
Lines;  together  with,  Experiments  on  the  Amorphous  Silica  of  Southern 
Illinois:  by  T.  R.  Ernest.     14  pages.     Postage  2  cents. 

8g.  Milbrig  Sheet  of  the  Lead  and  Zinc  District  of  Northwestern  Illinois: 
by  U.  S.  Grant  and  M.  J.  Perdue.     7  pages,  1  map,  1  plate.    Postage  2  cents. 

Circulars. 

Circular  No.  1.     The  Mineral  Production   of  Illinois   in  1905.     Pamphlet, 

14  pages,  postage  2  cents. 

Circular  No.  2.  The  Mineral  Production  of  Illinois  in  1906.  Pamphlet,  16 
pages,  postage  2  cents. 

Circular  No.  3.  Statistics  of  Illinois  Oil  Production,  1907.  Folder,  2  pages, 
postage  1  cent. 

Circular  No.  Jt.  The  Mineral  Production  of  Illinois  in  1901.  Pamphlet,  16 
pages,  postage  2  cents. 

Circular  No.  5.  The  Mineral  Production  of  Illinois  in  1908.  Pamphlet,  20 
pages,  postage  2  cents. 

—6  G 


82 


INDEX. 


Page. 

Acids,  ionization  constants  of •. 52 

Acknowledgments 10 

Analyses,  discussion  of 59 

results  of 54 

Anderson  Foundry  and  Machine  Co.,  acknowledgment  to 38 

Bond  of  sand-lime  bricks 14 

silica  bricks 13 

Calcium  carbonate,  dissociation  pressures  of '. 20 

Calcium  oxide,  hydration  of -22 

Carbon  dioxide,  vapor  pressures  of 20 

Cement,  Puzzolan,  character  of 18 

Chemical  analyses,  discussion  of : 59 

results  of 54 

Chemistry  of  sand-lime  bricks „ 47 

Clay  in  sand-lime  brick  mixtures 43 

Constitution  of  sand-lime  bricks 62 

Compression  tests  on  sand-lime  bricks 66 

Debray ,  cited : 20 

Definition  of  sand-lime  brick 14 

Experiments  with  sand-lime  bricks ' 39 

Feldspar  in  sand-lime  brick  mixtures 44 

Fire  resistance  of  sand-lime  bricks : . .  69, 71, 74 

Freezing  bricks,  effect  on 67 

German  sand-lime  brick  industry 12 

Hardening  of  sand-lime  bricks 45 

Heat  of  hydration  of  lime 29 

Hydration  of  calcium  oxide 22 

of  lime 29 

Hydraulic  mortar,  character  of 14 

Ionization  constants  of  acids 52 

LeChatelier,  cited 20 

Lime,  cost  of  burning 27 

dolomitic,  reactions  with 35 

heat  of  hydration  of 29 

impurities  in 26 

manufacture  of 26, 33 

market  grades  of 28 

origin  of 19 

pure,  reactions  with . . 35 

testing  of 29 

Michaelis,  Dr.  W.,  patent  of 12 

Mixtures  for  making  sand-lime  brick 31 

Molding,  pressure  in 44 

Mortar  bricks,  definition  of 1 1 

Feppcl,  S.  V. ,  cited • 36 


83 
Index — Concluded. 

Page. 

Pressures  on  dissociating  calcium  carbonate 20 

in  molding,  effect  of 44 

of  carbon  dioxide  vapor .*. 20 

Production  of  sand-lime  brick 13 

Puzzolan  cement .  character  of 18 

Kaw  materials  of  sand-lime  brick  industry 24 

Sand,  classification  of 25 

coarseness  of 37 

impurities  in 25,42 

occurrence  and  origin  of 24 

use  for  sand-lime  brick 24, 34 

Sand-lime  brick,  bond  of 14 

chemistry  of 47 

compression  test  s  on 66 

constituents  of 15 

constitution  of 62 

definition  of 14 

fire-resistance  of : 69, 71, 74 

hardening  of ' 45 

industry  in  America 12 

in  Germany 12 

statistics  of 13 

manufacture  of 31 

mixture,  preparation  of 31 

physical  texture  of 63 

raw  materials  of 24 

silica  in 15 

tests  of 36, 65 

Silica-brick,  character  of 15 

Silica  in  Illinois,  occurrence  of 9 

in  sand-lime  brick 15 

varieties  of 16 

Silicates,  derivation  of 17 

Silicic  acids,  character  of 17 

formulas  of 19 

Tests  of  sand-lime  bricks 65 

Texture  of  sand-lime  bricks 53 

Tricalcium  silicate,  origin  of 18 


